Unbihexium

Unbihexium, also known as element 126 or eka-plutonium, is the hypothetical chemical element with atomic number 126 and placeholder symbol Ubh. "Unbihexium" and "Ubh" are the temporary IUPAC name and symbol, respectively, until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table, unbihexium is expected to be a g-block superactinide and the eighth element in the 8th period. Unbihexium has attracted attention among nuclear physicists, especially in early predictions targeting properties of superheavy elements, for 126 may be a magic number of protons near the center of an island of stability, leading to longer half-lives, especially for 310Ubh or 354Ubh which may also have magic numbers of neutrons.
Early interest in possible increased stability led to the first attempted synthesis of unbihexium in 1971 and searches for it in nature in subsequent years. Despite several reported observations, more recent studies suggest that these experiments were insufficiently sensitive; hence, no unbihexium has been found naturally or artificially. Predictions of the stability of unbihexium vary greatly among different models; some suggest the island of stability may instead lie at a lower atomic number, closer to copernicium and flerovium.
Unbihexium is predicted to be a chemically active superactinide, exhibiting a variety of oxidation states from +1 to +8, and possibly being a heavier congener of plutonium. An overlap in energy levels of the 5g, 6f, 7d, and 8p orbitals is also expected, which complicates predictions of chemical properties for this element.
History.
Synthesis attempts.
The first and only attempt to synthesize unbihexium, which was unsuccessful, was performed in 1971 at CERN (European Organization for Nuclear Research) by René Bimbot and John M. Alexander using the hot fusion reaction:
High-energy (13-15 MeV) alpha particles were observed and taken as possible evidence for the synthesis of unbihexium. Subsequent unsuccessful experiments with higher sensitivity suggest that the 10 mb sensitivity of this experiment was too low; hence, the formation of unbihexium nuclei in this reaction was deemed highly unlikely.
Possible natural occurrence.
A study in 1976 by a group of American researchers from several universities proposed that primordial superheavy elements, mainly livermorium, unbiquadium, unbihexium, and unbiseptium, with half-lives exceeding 500 million years could be a cause of unexplained radiation damage (particularly radiohalos) in minerals. This prompted many researchers to search for them in nature from 1976 to 1983. A group led by Tom Cahill, a professor at the University of California at Davis, claimed in 1976 that they had detected alpha particles and X-rays with the right energies to cause the damage observed, supporting the presence of these elements, especially unbihexium. Others claimed that none had been detected, and questioned the proposed characteristics of primordial superheavy nuclei. In particular, they cited that the magic number "N" = 228 necessary for enhanced stability would create a neutron-excessive nucleus in unbihexium that might not be beta-stable, although several calculations suggest that 354Ubh may indeed be stable against beta decay. This activity was also proposed to be caused by nuclear transmutations in natural cerium, raising further ambiguity upon this claimed observation of superheavy elements.
Unbihexium has received particular attention in these investigations, for its speculated location in the island of stability may increase its abundance relative to other superheavy elements. Any naturally occurring unbihexium is predicted to be chemically similar to plutonium and may exist with primordial 244Pu in the rare earth mineral bastnäsite. In particular, plutonium and unbihexium are predicted to have similar valence configurations, leading to the existence of unbihexium in the +4 oxidation state. Therefore, should unbihexium occur naturally, it may be possible to extract it using similar techniques for the accumulation of cerium and plutonium. Likewise, unbihexium could also exist in monazite with other lanthanides and actinides that would be chemically similar. Recent doubt on the existence of primordial 244Pu casts uncertainty on these predictions, however, as the nonexistence (or minimal existence) of plutonium in bastnäsite will inhibit possible identification of unbihexium as its heavier congener.
The possible extent of primordial superheavy elements on Earth today is uncertain. Even if they are confirmed to have caused the radiation damage long ago, they might now have decayed to mere traces, or even be completely gone. It is also uncertain if such superheavy nuclei may be produced naturally at all, as spontaneous fission is expected to terminate the r-process responsible for heavy element formation between mass number 270 and 290, well before elements such as unbihexium may be formed.
A recent hypothesis tries to explain the spectrum of Przybylski's Star by naturally occurring flerovium, unbinilium, and unbihexium.
Naming.
Using the 1979 IUPAC recommendations, the element should be temporarily called "unbihexium" (symbol "Ubh") until it is discovered, the discovery is confirmed, and a permanent name chosen. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations are mostly ignored among scientists who work theoretically or experimentally on superheavy elements, who call it "element 126", with the symbol "E126", "(126)", or "126". Some researchers have also referred to unbihexium as "eka-plutonium", a name derived from the system Dmitri Mendeleev used to predict unknown elements, though such an extrapolation might not work for g-block elements with no known congeners, and "eka-plutonium" would instead refer to element 146 or 148 when the term is meant to denote the element directly below plutonium.
Difficulties in synthesis.
Every element from mendelevium onward was produced in fusion-evaporation reactions, culminating in the discovery of the heaviest known element oganesson in 2002 and most recently tennessine in 2010. These reactions approached the limit of current technology; for example, the synthesis of tennessine required 22 milligrams of 249Bk and an intense 48Ca beam for six months. The intensity of beams in superheavy element research cannot exceed 1012 projectiles per second without damaging the target and detector, and producing larger quantities of increasingly rare and unstable actinide targets is impractical.
Consequently, future experiments must be done at facilities such as the under-construction superheavy element factory (SHE-factory) at the Joint Institute for Nuclear Research (JINR) or RIKEN, which will allow experiments to run for longer stretches of time with increased detection capabilities and enable otherwise inaccessible reactions. Even so, it will likely be a great challenge to synthesize elements beyond unbinilium (120) or unbiunium (121), given their short predicted half-lives and low predicted cross sections.
It has been suggested that fusion-evaporation will not be feasible to reach unbihexium. As 48Ca cannot be used beyond elements 118 or possibly 119, the only alternatives are increasing the atomic number of the projectile or studying symmetric or near-symmetric reactions. One calculation suggests that the cross section for producing unbihexium from 249Cf and 64Ni may be as low as nine orders of magnitude lower than the detection limit; such results are also suggested by the non-observation of unbinilium and unbibium in reactions with heavier projectiles and experimental cross section limits. If "Z" = 126 represents a closed proton shell, compound nuclei may have greater survival probability and the use of 64Ni may be more feasible for producing nuclei with 122 < "Z" < 126, especially for compound nuclei near the closed shell at "N" = 184. However, the cross section still might not exceed 1 fb, posing an obstacle that may only be overcome with more sensitive equipment.
Predicted properties.
Nuclear stability and isotopes.
Extensions of the nuclear shell model predicted that the next magic numbers after "Z" = 82 and "N" = 126 (corresponding to 208Pb, the heaviest stable nucleus) were "Z" = 126 and "N" = 184, making 310Ubh the next candidate for a doubly magic nucleus. These speculations led to interest in the stability of unbihexium as early as 1957; Gertrude Scharff Goldhaber was one of the first physicists to predict a region of increased stability in the vicinity of, and possibly centered at, unbihexium. This notion of an "island of stability" comprising longer-lived superheavy nuclei was popularized by University of California professor Glenn Seaborg in the 1960s.
In this region of the periodic table, "N" = 184 and "N" = 228 have been suggested as closed neutron shells, and various atomic numbers, including "Z" = 126, have been proposed as closed proton shells. The extent of stabilizing effects in the region of unbihexium is uncertain, however, due to predictions of shifting or weakening of the proton shell closure and possible loss of double magicity. More recent research predicts the island of stability to instead be centered at beta-stable isotopes of copernicium (291Cn and 293Cn) or flerovium ("Z" = 114), which would place unbihexium well above the island and result in short half-lives regardless of shell effects.
Earlier models suggested the existence of long-lived nuclear isomers resistant to spontaneous fission in the region near 310Ubh, with half-lives on the order of millions or billions of years. However, more rigorous calculations as early as the 1970s yielded contradictory results; it is now believed that the island of stability is not centered at 310Ubh, and thus will not enhance the stability of this nuclide. Instead, 310Ubh is thought to be very neutron-deficient and susceptible to alpha decay and spontaneous fission in less than a microsecond, and it may even lie at or beyond the proton drip line. A 2016 calculation on the decay properties of 288-339Ubh upholds these predictions; the isotopes lighter than 313Ubh (including 310Ubh) may indeed lie beyond the drip line and decay by proton emission, 313-327Ubh will alpha decay, possibly reaching flerovium and livermorium isotopes, and heavier isotopes will decay by spontaneous fission. This study and a quantum tunneling model predict alpha-decay half-lives under a microsecond for isotopes lighter than 318Ubh, rendering them impossible to identify experimentally. Hence, the isotopes 318-327Ubh may be synthesized and detected, and may even constitute a region of increased stability against fission around "N" ~ 198 with half-lives up to several seconds.
Beyond this point, a "sea of instability" defined by very low fission barriers (caused by greatly increasing Coulomb repulsion in superheavy elements) and consequently fission half-lives on the order of 10−18 seconds are predicted among various models. Although the exact limit of stability for half-lives over one microsecond varies, stability against fission is strongly dependent on the "N" = 184 and "N" = 228 shell closures and rapidly drops off immediately beyond the influence of the shell closure. Such an effect may be reduced, however, if nuclear deformation in intermediate isotopes may lead to a shift in magic numbers; a similar phenomenon was observed in the deformed doubly magic nucleus 270Hs. This shift could then lead to longer half-lives, perhaps on the order of days, for isotopes such as 342Ubh that would also lie on the beta-stability line. A second island of stability for spherical nuclei may exist in unbihexium isotopes with many more neutrons, centered at 354Ubh and conferring additional stability in "N" = 228 isotones near the beta-stability line. Originally, a short half-life of 39 milliseconds was predicted for 354Ubh toward spontaneous fission, though a partial alpha half-life for this isotope was predicted to be 18 years. More recent analysis suggests that this isotope may have a half-life on the order of 100 years should the closed shells have strong stabilizing effects, placing it at the peak of an island of stability. It may also be possible that 354Ubh is not doubly magic, as the "Z" = 126 shell is predicted to be relatively weak, or in some calculations, completely nonexistent. This suggests that any relative stability in unbihexium isotopes would be only due to neutron shell closures that may or may not have a stabilizing effect at "Z" = 126.
Chemical.
Unbihexium is expected to be the sixth member of a superactinide series. It may have similarities to plutonium, as both elements have eight valence electrons over a noble gas core. In the superactinide series, the Aufbau principle is expected to break down due to relativistic effects, and an overlap of the energy levels of the 7d, 8p, and especially 5g and 6f orbitals is expected, which renders predictions of chemical and atomic properties of these elements very difficult. The ground state electron configuration of unbihexium is thus predicted to be [Og] 5g2 6f3 8s2 8p1 or 5g1 6f4 8s2 8p1, in contrast to [Og] 5g6 8s2 derived from Aufbau.
As with the other early superactinides, it is predicted that unbihexium will be able to lose all eight valence electrons in chemical reactions, rendering a variety of oxidation states up to +8 possible. The +4 oxidation state is predicted to be most common, in addition to +2 and +6. Unbihexium should be able to form the tetroxide UbhO4 and hexahalides UbhF6 and UbhCl6, the latter with a fairly strong bond dissociation energy of 2.68 eV. It may also be possible for unbihexium to form a stable monofluoride UbhF. Calculations suggest that a diatomic UbhF molecule will feature a bond between the 5g orbital in unbihexium and the 2p orbital in fluorine, thus characterizing unbihexium as an element whose 5g electrons should actively participate in bonding. It is also predicted that the Ubh6+ (in particular, in UbhF6) and Ubh7+ ions will have the electron configurations [Og] 5g2 and [Og] 5g1, respectively, in contrast to the [Og] 6f1 configuration seen in Ubt4+ and Ubq5+ that bears more resemblance to their actinide homologs. The activity of 5g electrons may influence the chemistry of superactinides such as unbihexium in new ways that are difficult to predict, as no known elements have electrons in a "g" orbital in the ground state.


Molar ionization energies of the elements

These tables list values of molar ionization energies, measured in kJ⋅mol−1. This is the energy per mole necessary to remove electrons from gaseous atoms or atomic ions. The first molar ionization energy applies to the neutral atoms. The second, third, etc., molar ionization energy applies to the further removal of an electron from a singly, doubly, etc., charged ion. For ionization energies measured in the unit eV, see "Ionization energies of the elements (data page)". All data from rutherfordium onwards is predicted.


Neltenexine

Neltenexine (trade name Alveoten) is a mucolytic.


Diphenylzinc

Diphenylzinc is an organozinc compound. It is commonly used as the synthetic equivalent of a Ph− synthon. Solvent-free diphenylzinc exists as dimeric molecules in the solid state.
Diphenylzinc is commercially available. It may be prepared by reaction of phenyllithium with zinc bromide:
It may also be prepared by the reaction of phenylmagnesium bromide with zinc chloride or diphenylmercury with zinc metal.


Bromodiphenylmethane

Bromodiphenylmethane or 1,1'-(bromomethanediyl)dibenzene, is an organobromine compound with the chemical formula .


Magnesium lactate

Magnesium lactate, the magnesium salt of lactic acid, is a mineral supplement.
Added to some food and beverages as an acidity regulator and labeled as E329.


Unsepttrium


Sodium hydrogenoxalate

Sodium hydrogenoxalate is the sodium salt of hydrogenoxalate. The only difference from oxalic acid is that one of the two hydrogen atoms has been replaced with a sodium atom. Like oxalate, it is toxic for the kidney function if swallowed because of the precipitation of poorly soluble calcium oxalate stones that can obstruct the kidney tubules.
Stability.
Upon being heated, sodium hydrogenoxalate undergoes cation-pairing to become oxalic acid and sodium oxalate, the latter of which decomposes into sodium carbonate and carbon monoxide.


Triethylindium

Triethylindium is an
organometallic compound. Its chemical formula is .
Synthesis.
This compound can be obtained by reacting indium(III) chloride with a diethyl ether solution of ethyl magnesium chloride:
Other routes are also known.
Properties.
Indium triethyl is a colorless, toxic, oxidation and hydrolysis-sensitive liquid. It is a monomer in the gaseous and dissolved state. The compound reacts with halomethanes to form diethyl indium halides.
Triethylindium is highly reactive with water:
Applications.
Indium triethyl is used to prepare indium phosphide layers for microelectronics.


Sekaninaite

Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a silicate mineral, the iron-rich analogue of cordierite.
It was first described in 1968 for an occurrence in Dolní Bory, Vysočina Region, Moravia, Czech Republic, and is now known also from Ireland, Japan, and Sweden. It was named after a Czech mineralogist, Josef Sekanina (1901–1986). In Brockley on Rathlin Island, Ireland sekaninaite occurs in bauxitic clay within the contact aureole of a diabase intrusive plug.
Structure and composition.
The chemical formula of sekaninaite is: <chem>(Fe^2+, Mg^2+)2[Al4Si5O18]*\mathit{n}H2O</chem>. Grapes calculated the percentage weights of the sample from Dolni Bory,
This compound exists in nature in the form of two polymorphs: one having a disordered hexagonal structure and the other arranged in an ordered orthorhombic structure. As an aluminosilicate, the repeated and ordered structure is based on polymerization of one or the other's tetrahedral framework of Si, Al tetrahedra (Yakubovich, 2003). Nearly all analyses show excess of Al and deficiency in Si with respect to tetrahedral components. The overall substitution of alkalis causes excess in cations found in (K2O, Na2O, CaO), implying that sekaninaite is essentially anhydrous (Grapes, 2010).
The atomic structures of cordierites are interpreted as a continuous series of structures that vary based on the content of octahedrally coordinated Mg and Fe cations. The varying content of atoms in the octahedral M position has an effect on the orthorhombic unit cell's parameters. The wide range of isomorphism of Mg and Fe(4-96%) suggest the existence of a continuous isomorphic series cordierite <chem>(Mg,Fe)2[Al4Si4O18]*\mathit{n}H2O</chem>-sekaninaite <chem>(Fe,Mg)2[Al4Si4O18]*\mathit{n}H2O</chem>. It is shown via crystallographic data that a shift in the iron content leads to a corresponding variance in a and b unit cell parameters (Yakubovich, 2003). As an aluminosilicate/cyclosilicate, the octahedral M-O distances consist of 5 independent tetrahedra form a 3-dimensional anionic framework of ordered and distributed Al3+ and Si4+ cations. One independent AlO4 and two SiO4 vortex-sharing tetrahedra share oxygen atoms to form six-member rings along the c axis of the unit cell. Mg, Fe octahedra share edges with SiO4 to form rings from alternating octahedra and tetrahedra. Thus, the framework can be described as a semi-layered structure formed of layers of tetrahedra linked into rings by sharing vertices and octahedra and tetrahedra sharing edges, alternating along the c axis. The distortion of the orthorhombic unit cell is determined by the chemical composition rather than the degree of ordering in the tetrahedral framework (Yakubovich, 2003). The temperature at which the liquidous phases crystallize in a sequence: mullite + tridymite, followed by sekaninaite and finally fayalite + clinoferrosilite (Grapes, 2010). Similar trends are observed for amphiboles, clinopyroxenes, olivines, and others. The increase in the Fe mole fraction of minerals was not related with iron input, but was caused by its redistribution during contact metamorphism (Korchak, 2010).
Physical properties.
Stanek and Miskovsky (1975) first identified and diagnosed sekaninaite as a new mineral in the cordierite series. They sampled the poorly developed crystals of the Dolni Bory region, Czechoslovakia, where specimen did not exceed 70 cm. Dolni Bory samples are very different from samples found in the Kuznetsk paralavas. They are very close analogues with respect to Mg/Fe ratios but vastly different a-, b- and c- parameters (Grapes, 2010). Grapes and colleagues calculated cell dimension to be a 17.230(5), b 9.835(3), c 9.314(3) A. The colour of sekaninaite is bright blue and distinctly pleochroic with X = colourless; Y = blue; Z = pale blue; absorption occurs in the sequence Y > Z > X. Sekaninaite has a hardness of 7-7.5; it cleaves imperfectly along {100} and exhibits parting on {001} (Fleischer, 1977). Majority of crystals show zonation (Fe increasing from core to rim). It common twinned on {110} and {310}, simulating hexagonal symmetry. Sekaninaite is classified under the space group Cccm; it is an orthorhombic crystal that is found in series with cordierite (Stanek, 1975).
Geologic occurrence and location.
Sekaninaite was first discovered in the Dolni Bory region of the Czech Republic. Its occurrence is in the albite zone of pegmatite in granulites and gneisses (Fleischer, 1977). Sekaninaite is found in pyrometamorphic rocks, extensively rocks formed via process of ancient combustion metamorphism; paralavas, clinkers and buchites. These combustion metamorphic rocks occur in clinker beds and breccias of vitrified sandstone-siltstone clinker fragments cemented by paralava. These partially baked and oxidized psammitic-pelitic sediments are associated with burnt coal seams, belonging to places like the Kuznetsk coal basin, Siberia (Grapes, 2010). Sekaninaite-Fe-cordierite exists in series and is largely dependent upon variations in solid solution. These minerals are more prevalent in paralavas found in: Power River, Wyoming, Ravat area, Tajikistan, Kenderlyk Basin, eastern Kazakhstan and the Djhar basin in India; each differ in sedimentary mineral assemblage and results depend on high-temperature fusion of mixtures of sandstone-siltstone and minor ferruginous components (Grapes, 2010). These Fe-rich paralavas are composed of Fe-olivine, esseneite, dorite, melilite, Fe-cordierite, anorthite, spinel, tridymite, fayalite, magnetite, quartz etc. (Novikova, 2008).


Dibromodiethyl sulfide

Dibromodiethyl sulfide is a chemical like mustard gas in which bromine replaces chlorine. It is very irritating as a vapour.
Production.
Dibromodiethyl sulfide can be produced by the reaction of bromine with thiodiglycol.
Properties.
Dibromodiethyl sulfide takes the form of white crystals. The melting point is between 31 and 34°C. It decomposes when heated to 240°C.
The fungus "Tyromyces palustris" can split the molecule at the sulfur.


Weeksite

Weeksite is a naturally occurring uranium silicate mineral with the chemical formula: K2(UO2)2Si6O15•4(H2O), potassium uranyl silicate. Weeksite has a Mohs hardness of 1-2. It was named for USGS mineralogist Alice Mary Dowse Weeks (1909–1988).
Appearance.
Weeksite is visually similar to other uranium minerals such as carnotite and zippeite, both being encrustations that form on other rocks (usually sandstones or limestones).
Occurrence.
Weeksite was first described in 1960 for an occurrence on Topaz Mountain, Thomas Range, Juab County, Utah.
Weeksite occurs within small "opal" veins within rhyolite and agglomerates, and as encrustations in sandstones and limestones. It occurs associated with opal, chalcedony, calcite, gypsum, fluorite, uraninite, thorogummite, uranophane, boltwoodite, carnotite and margaritasite.


Diphosphagermylene

Diphosphagermylenes are a class of compounds containing a divalent germanium atom bound to two phosphorus atoms. While these compounds resemble diamidocarbenes, such as N-heterocyclic carbenes (NHC), diphosphagermylenes display bonding characteristics distinct from those of diamidocarbenes. In contrast to NHC compounds, in which there is effective N-C p(π)-p(π) overlap between the lone pairs of planar nitrogens and an empty p-orbital of a carbene, systems containing P-Ge p(π)-p(π) overlap are rare. Until 2014, the geometry of phosphorus atoms in all previously reported diphosphatetrylenes are pyramidal, with minimal P-Ge p(π)-p(π) interaction. It has been suggested that the lack of p(π)-p(π) in Ge-P bonds is due to the high energetic barrier associated with achieving a planar configuration at phosphorus, which would allow for efficient p(π)-p(π) overlap between the phosphorus lone pair and the empty P orbital of Ge. The resulting lack of π stabilization contributes to the difficulty associated with isolating diphosphagermylene and the Ge-P double bonds. However, utilization of sterically encumbering phosphorus centers has allowed for the isolation of diphosphagermylenes with a planar phosphorus center with a significant P-Ge p(π)-p(π) interaction.
Preparation of Diphosphagermylenes.
Synthesis of P-Ge σ-Only Diphosphagermylenes.
Reactivity of sterically demanding lithium (fluorosilyl)silylphosphanides with GeI2 yields green, cubic crystals in moderate yield. The identity of this species was investigated using only multinuclear NMR, elemental analysis, and UV-vis. Computational calculations (at the CIS level with the ab initio Los Alamos pseudopotential method (LAN L 1 DZ)) of the diphosphagermylene electronic structure was in agreement experimentally-derived electronic transition values. Due to disorder, the crystal structure of the diphosphagermylene could not be investigated.
Synthesis of P-Ge π-Stabilized Diphosphagermylenes.
The sterically encumbered germylene ligand (Dipp)2PH, where Dipp=2,6-iPr2C6H3, was synthesized by the addition of PCl3 to DippLi-(OEt2), followed by the addition of LiAlH4. (Dipp)2PH was added to PhCH2K, which is combined with GeCl2 to provide (Dipp2P)2Ge. The synthesis resulted in dark red crystals suitable for x-ray crystallography. The identity of the compound was confirmed by elemental analysis, multinuclear NMR, and x-ray crystallography. This compound is stable in the absence of air and water.
Structure and Bonding.
P-Ge σ-only system: Driess's diphosphagermylene.
While crystals were formed of Driess's diphosphagermylene, the X-ray structure diphosphagermylene could not be analyzed due to disordering. It has been suggested that the three lone pairs in Driess's diphosphagermylene system are composed of Ge (4s, 4p) and P (3s, 3p) valence orbitals. Driess calculated (MP2/DZ+POL//RHF/DZ+ZPE) the reaction profile for the isomerization of E(PH2)2 (E = Si, Ge, Sn, Pb) from a σ-only, carbene-like system to a tautomer containing trivalent E with a π bond between E and phosphorus. The authors observed that the carbene-like form is preferred over its tautomer for silicon, germanium, tin, and lead analogues.
P-Ge p(π)-p(π) Stabilized Systems: ((Dipp)2P)2Ge and ((Tripp)2P)2Ge.
P-substituted heavier group 14 analogues (Si, Ge, Sn, Pb) of diaminocarbenes are less established. It has been suggested this is due to a high energetic barrier associated with achieving a planar configuration at phosphorus, which would enable p(π)-p(π) overlap between the P lone pair and the empty p orbital of the group 14 center. Differences in donation ability of phosphorus versus nitrogen likely do not play a role in achieving p(π)-p(π) overlap because calculations indicate that the π donor capacity of phosphorus is similar to that of nitrogen. Consequently, all P atoms in reports on diphosphatetrylenes previous to ((Dipp)2P)2Ge contain pyramidal P with Ge-P bonds of exclusively σ character. By utilizing sterically encumbered (Dipp)P ligands, p(π)-p(π) in diphosphagermylene was achieved. This compound crystallizes as discrete monomers and is the first crystallographically characterized diphosphagermylene with a two-coordinate Ge center.
By crystal structure analysis, the bond lengths of the two germanium-phosphorus bonds are 2.2337 Å (P1-Ge) and 2.3823 Å (P2-Ge). While the phosphorus center of P1-Ge is pyramidal, the P2-Ge phosphorus is trigonal planar. Moreover, the planes of P1-Ge-P2 and C-P1-Ge are nearly in coincident. These results are consistent with multiple bond character between a trigonal planar phosphorus (P1) and Ge. It has been suggested that only one P of the diphosphagermylene is planar because there is competition between the two phosphorus lone pairs and the empty P orbitals at the Ge center if both phosphorus atoms are planar. This would result in a weaker P-Ge interaction that would not be sufficient to overcome the energy of planarizing both P atoms.
In addition, ((Dipp)2P)2Ge was modified such that an iPr groups was added to the para position of (Dipp)2P, to make (Tripp)2P. The donating effect of an additional iPr group has little effect on the bonding and structure of the diphosphagermylene.
Solution and Solid State Nuclear Magnetic Resonance (NMR).
A single, broad singlet is observed at 3.2 ppm at room temperature in the solution state phosphorus nuclear magnetic resonance (PNMR) of ((Dipp)2P)2Ge. This signal is consistent with rapid exchange between the planar and pyramidal phosphorus centers. As the temperature is reduced to -80 C, the signal becomes two broad, equal intensity singlets at -42.0 ppm and 8.0.
Two peaks with isotropic chemical shifts of 81.9 and -61.6 ppm, in a 1:1 ratio are observed in the solid state PNMR. No other signals are observed in the PNMR. In general diphosphagermylenes with pyramidal phosphorus centers exhibit a chemical shift close to those of free phosphine. In addition, planar phosphorus centers of GeIV=P compounds generally have a downfield PNMR shift. Consequently, peaks at 81.9 and -61.6 ppm have been assigned as planar and pyramidal phosphorus centers of ((Dipp)2P)2Ge, respectively. This has been supported by DFT calculations that predict PNMR shifts of planar and pyramidal phosphorus centers of ((Dipp)2P)2Ge are at 100 and -61 ppm.
Natural Bond Orbital (NBO) Analysis.
Natural bond orbital analysis has been carried out on the P-Ge p(π)-p(π) system, ((Dipp)2P)2Ge. Inspection of the molecular orbitals reveals that the HOMO-1 consists of a π orbital, resulting from donation from the planar P lone pair into the empty P orbital of the germylene center. Natural bond orbital analysis reveals that this bond is 77% P-based and 0.3 eV higher in energy than the P-Ge σ bond. In contrast, the lone pair of the pyramidal phosphorus center is essentially sp hybridized and directed away from the germanium center. The germanium lone pair is predominantly s-character. Wiberg bond indices for Ge-P1 and Ge-P2 bonds are 1.33 and 0.89, respectively, which is consistent with a double bond between Ge-P1 and a single bond between Ge-P2.
Atoms in Molecules (AIM) Analysis.
AIM analysis of ((Dipp)2P)2Ge suggests that there is a double bond between P1-Ge. Bond order can be assessed by measuring the ellipticity, a measure of anisotropic electron density, at the bond critical point. For example, butane, ethylene, and ethyne have a bond ellipticity of 0.01, 0.30, and 0.00 respectively, which correspond to a single, double, and a triple bond. A bond critical point between P1-Ge with ρ=0.091 and ellipticity 0.297 was observed in ((Dipp)2P)2Ge, consistent with a double bond. . This contrasts ρ=0.083 and ellipticity 0.064 at the bond critical point of P2-Ge in ((Dipp)2P)2Ge. Delocalization index (DI) was also used to predict the bond order of ((Dipp)2P)2Ge. DI values for P1-Ge and P2-Ge were determined to be 1.275 and 0.843, consistent with a P1-Ge double bond and Wiberg bond indices calculated.


Wakabayashilite

Wakabayashilite is a rare arsenic, antimony sulfide mineral with formula [(As,Sb)6S9][As4S5].
Discovery and occurrence.
Wakabayashilite is a rare mineral first discovered in Nevada in the 1920s, but it was mistaken for a hair orpiment. In the 1970s, wakabayashilite was found in Japan and scientifically identified as a new mineral. It was named after Yaichiro Wakabayashi (1874–1943), a Japanese mineralogist of the Mitsubishi Mining Company in Japan. Wakabayashilite has been discovered later in several places around the world such as in Saha Republic (Russia), Zhuang region (China) and Hautes-Alpes (France). In the United States, Wakabayashilite has been found at the White Caps Mine, in the Toquima Range of mountains, Nye County, Nevada. Other Nevada locations where the mineral has been found include the Getchel Mine, in the Osgood Mountains, Humboldt County, and at the Seminole-Regent Mine, in the Rawhide Mining District, Mineral County. Originally, Wakabayashilite was found in druses of quartz associated with orpiment and realgar, however, it was later found embedded in calcite as well. Generally, it mostly occurs with other arsenic minerals in high-arsenic gold deposits.
Structure and optical properties.
Even though Wakabayashilite possesses the hexagonal pseudosymmetry, it actually belongs to the orthorhombic crystal system meaning it contains three axes of different length but are mutually perpendicular to one another. It also belongs to the space group Pna21. For its optical properties, Wakabayashilite is a biaxial mineral and its color in plane polarized light is golden-yellow to lemon-yellow and it also has strong pleochroism.
For now, since wakabayashilite is rare, it is of no obvious economical interest. However, there have been some recent research conducted on its interesting structure, pseudosymmetry and twinning.


Wolframite

Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite is found in quartz veins and pegmatites associated with granitic intrusives. Associated minerals include cassiterite, scheelite, bismuth, quartz, pyrite, galena, sphalerite, and arsenopyrite.
This mineral was historically found in Europe in Bohemia, Saxony, and Cornwall. China reportedly has the world's largest supply of tungsten ore with about 60%. Other producers are Canada, Portugal, Russia, Australia, Thailand, South Korea, Rwanda, Bolivia, the United States, and the Democratic Republic of the Congo.
Name.
The name "wolframite" is derived from German ""wolf rahm", the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from "Lupi spuma"", the name Georg Agricola used for the element in 1546, which translates into English as "wolf's froth" or "cream". The etymology is not entirely certain but seems to be a reference to the large amounts of tin consumed by the mineral during its extraction, the phenomenon literally being likened to a wolf eating a sheep. Wolfram is the basis for the chemical symbol "W" for tungsten as a chemical element.
Use.
Wolframite is highly valued as the main source of the metal tungsten, a strong and quite dense material with a high melting temperature used for electric filaments and armor-piercing ammunition, as well as hard tungsten carbide machine tools. During World War II, wolframite mines were a strategic asset, due to its use in munitions and tools.
Wolframite was considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of the Congo, during the Congo Wars.


Cyanuric bromide

Cyanuric bromide is a heterocyclic compound with formula C3N3Br3. It contains a six-membered ring of alternating nitrogen and carbon atoms, with a bromine atom attached to each carbon. It is formed by the spontaneous trimerisation of cyanogen bromide.
Reactions.
Cyanuric bromide can be used to synthesize substituted triazines. For example it reacts with anilines to form derivatives of melamine. With ammonia, melamine is produced. Primary or secondary amines react. Cyanuric trihydrazide is produced in the reaction with hydrazine. When heated with urea at 140°C, ammelide is formed.
Cyanuric bromide reacts with water, particularly in alkaline conditions to cyanuric acid and hydrogen bromide.
Cyanuric bromide can add bromine to other compound, and when it is heated with acetic acid, acetyl bromide is produced.
Formation.
Cyanuric bromide can formed in a reaction with potassium ferrocyanide with bromine at 200°C. The trimerization reaction of cyanogen bromide (BrCN) is catalyzed by aluminium trichloride or hydrogen bromide.


Iron(III) oxide-hydroxide

Iron(III) oxide-hydroxide or ferric oxyhydroxide is the chemical compound of iron, oxygen, and hydrogen with formula .
The compound is often encountered as one of its hydrates, ·"n" [rust]. The monohydrate · (CAS , C.I. 77492) is often referred to as iron(III) hydroxide , hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42.
Natural occurrences.
Anhydrous ferric hydroxide occurs in the nature as the exceedingly rare mineral bernalite, Fe(OH)3·"n"H2O (n=0.0-0.25). Iron oxyhydroxides, , are much more common and occur naturally as structurally different minerals (polymorphs) denoted by the Greek letters α, β, γ and δ.
Goethite and lepidocrocite, both crystallizing in orthorhombic system, are the most common forms of iron(III) oxyhydroxide and the most important mineral carriers of iron in soils.
Iron(III) oxyhydroxide is the main component of other minerals and mineraloids:
Properties.
The color of iron(III) oxyhydroxide ranges from yellow through dark-brown to black, depending on the degree of hydration, particle size and shape, and crystal structure.
Structure.
The crystal structure of β- (akaganeite) is that of hollandite or . The unit cell is tetragonal with "a"=1.048 and "c"=0.3023 nm, and contains eight formula units of FeOOH. Its dimensions are about 500 × 50 × 50 nm. Twinning often produces particles with the shape of hexagonal stars.
Chemistry.
On heating, β- decomposes and recrystallizes as α- (hematite).
Uses.
Limonite, a mixture of various hydrates and polymorphs of ferric oxyhydroxide, is one of the three major iron ores, having been used since at least 2500 BC.
Yellow iron oxide, or Pigment Yellow 42, is Food and Drug Administration (FDA) approved for use in cosmetics and is used in some tattoo inks.
Iron oxide-hydroxide is also used in aquarium water treatment as a phosphate binder.
Iron oxide-hydroxide nanoparticles have been studied as possible adsorbents for lead removal from aquatic media.
Production.
Iron(III) oxyhydroxide precipitates from solutions of iron(III) salts at pH between 6.5 and 8.
Thus the oxyhydroxide can be obtained in the lab by reacting an iron(III) salt, such as ferric chloride or ferric nitrate, with sodium hydroxide:
In fact, when dissolved in water, pure will hydrolyze to some extent, yielding the oxyhydroxide and making the solution acidic:
Therefore, the compound can also be obtained by the decomposition of acidic solutions of iron(III) chloride held near the boiling point for days or weeks:
(The same process applied to iron(III) nitrate or perchlorate solutions yields instead particles of α-.)
Another similar route is the decomposition of iron(III) nitrate dissolved in stearic acid at about 120 °C.
The oxyhydroxide prepared from ferric chloride is usually the β polymorph (akaganeite), often in the form of thin needles.
The oxyhydroxide can also be produced by a solid-state transformation from iron(II) chloride tetrahydrate ·4.
The compound also readily forms when iron(II) hydroxide is exposed to air:
The iron(II) hydroxide can also be oxidized by hydrogen peroxide in the presence of an acid:
Safety.
The risk and safety phrases for iron oxides are , , , , and .


Bonaccordite

Bonaccordite is a rare mineral discovered in 1974. Its chemical formula is Ni2FeBO5 and it is a mineral of the ludwigite group. It usually crystallizes in long, cylindrical prisms that form within another source. It is named after the area of Bon Accord, where it was first found. There have also been findings of bonaccordite within nuclear plants at multiple companies. It builds up a deposit within the machines and is a very hard mineral to clean out because it is resistant to ordinary techniques.
History.
Bonaccordite was first described in 1974 for an occurrence in the Bon Accord area, Barberton, Transvaal, South Africa. It occurs in a tabular nickeliferous serpentinite, on the margin of an ultramafic intrusive. The actual site of the bonaccordite finding is a possible meteorite site three kilometers west of the Scotia talc mine.
Composition.
The chemical formula for bonaccordite is Ni2FeBO5.
The two analysts confirmed the presence of boron by using the wet-chemical analysis.
Geologic occurrence.
Bonaccordite can occur as either a cluster of thin, long prisms or rosette-like radiating groups. The prisms can form veins through other minerals and the radiating groups can occur in minerals like liebenbergite or trevorite. Bonaccordite usually occurs along with trevorite, liebenbergite, népouite, nimite, gaspeitev, and millerite in the area of Bon Accord. All of these minerals crystallize as slender prisms.
Physical properties.
Bonaccordite is an opaque mineral with a reddish-brown color. In reflected light, the color is grey with a brownish tinge with strong, reddish-brown internal reflections. In many cases, bonaccordite crystallizes into long, slender cylinders. It has been discovered to be the nickel analogue of ludwigite.
The Mohs hardness for bonaccordite is 7 and its density is 5.17 g/cm3. The optical class is biaxial. Bonaccordite has an orthorhombic crystal system with a point group of 2/m 2/m 2/m. The crystals are structured as elongated prisms within another material. There has been no observed cleavages or twinning. Space group has been determined as ["Pbam"] and cell dimensions were calculated to a = 9.213(6) b = 12.229(7) c = 3.001(2) Z = 4.
Bonaccordite is insoluble and has only shown reactivity to hydrochloric acid. It is very hard to clean it off of fuel rods in nuclear power reactors where it is sometimes formed.
It has been shown to form hydrothermally in near-supercritical water at temperatures above 350 °C and in presence of alkaline conditions. Its formation in PWR reactors can be accelerated by lithium produced in 10B(n,α)7Li reaction with boron in coolant. Bonaccordite can be an indicator of Axial-Offset-Anomaly of neutron flux and power density in PWR power plants.


Plumbylene

Plumbylenes (or plumbylidenes) are divalent organolead(II) analogues of carbenes, with the general chemical formula, R2Pb, where R denotes a substituent. Plumbylenes possess 6 electrons in their valence shell, and are considered open shell species.
The first plumbylene reported was the dialkylplumbylene, [(Me3Si)2CH]2Pb, which was synthesized by Michael F. Lappert "et al" in 1973.
Plumbylenes may be further classified into carbon-substituted plumbylenes, plumbylenes stabilized by a group 15 or 16 element, and monohalogenated plumbylenes (RPbX).
Synthesis.
Plumbylenes can generally be synthesized via the transmetallation of PbX2 (where X denotes halogen) with an organolithium (RLi) or Grignard reagent (RMgX). The first reported plumbylene, [((CH3)3Si)2CH]2Pb, was synthesized by Michael F. Lappert "et al" by transmetallation of PbCl2 with [((CH3)3Si)2CH]Li. The addition of equimolar RLi to PbX2 produces the monohalogenated plumbylene (RPbX); addition of 2 equivalents leads to disubstituted plumbylene (R2Pb). Adding an organolithium or Grignard reagent with a different organic substituent (i.e. R’Li/R’MgX) from RPbX leads to the synthesis of heteroleptic plumbylenes (RR’Pb). Dialkyl-, diaryl-, diamido-, dithioplumbylenes, and monohalogenated plumbyelenes have been successfully synthesized this way.
Transmetallation with [((CH3)3Si)2N]2Pb as the Pb(II) precursor has also been used to synthesize diarylplumbylenes, disilylplumbylenes, and saturated "N"-heterocyclic plumbylenes.
Alternatively, plumbylenes may be synthesized from the reductive dehalogenation of tetravalent organolead compounds (R2PbX2).
Structure and bonding.
The key aspects of bonding and reactivity in plumbylenes are dictated by the inert pair effect, whereby the combination of a widening s–p orbital energy gap as a trend down the group 14 elements and a strong relativistic contraction of the 6s orbital lead to a limited degree of sp hybridization and the 6s orbital being deep in energy and inert. Consequently, plumbylenes exclusively have a singlet spin state due to the large singlet–triplet energy gap, and tend to exist in an equilibrium between monomeric and dimeric forms in solution. This is in contrast to carbenes, which often have a triplet ground state and readily dimerize to form alkenes.
In dimethyllead, (CH3)2Pb, the Pb–C bond length is 2.267 Å and the C–Pb–C bond angle is 93.02°; the singlet–triplet gap is 36.99 kcal mol−1.
Diphenyllead, (C6H5)2Pb was computed with GAMESS at the B3PW91 level of theory using the basis sets 6-311+G(2df,p) for C and H and def2-svp for Pb with the ECP60MDF pseudopotential, in an adapted procedure (which uses the cc-pVTZ basis set for Pb instead). The molecular orbitals (MOs) (visualized using Chimera) and natural bond orbitals (NBOs) (visualized using multiwfn) generated are produced below, and qualitatively identical to the literature. As expected, the HOMO is 6s-dominated, and the LUMO is 6p-dominated. The NBOs are of the 6s lone pair and vacant 6p orbital respectively.
The Pb–C bond distance was found to be 2.303 Å and the C–Pb–C angle 105.7°. Notwithstanding the different levels of theory, the larger bond angle for (C6H5)2Pb compared to can be rationalized by the greater repulsion between the sterically bulkier phenyl groups relative to methyl groups.
Atoms in molecules (AIM) topology analysis revealed critical points in (C6H5)2Pb, and is consistent with the literature.
Plumbylenes occur as reactive intermediates in the formation of tetravalent plumbanes (R4Pb). Although the inert pair effect suggests the divalent state should be thermodynamically more stable than the tetravalent state, in the absence of stabilizing substituents, plumbylenes are sensitive to heat and light, and tend to undergo polymerization and disproportionation, forming elemental lead in the process.
Plumbylenes can be stabilized as monomers by the use of sterically bulky ligands (kinetic stabilization) or heteroatom-containing substituents that can donate electron density into the vacant 6p orbital (thermodynamic stabilization).
Dimerization.
Plumbylenes are able to undergo dimerization in two ways: either through the formation of a Pb=Pb double bond to form a formal diplumbene, or through bridging halide interactions. Unhalogenated plumbylenes tend to exist in an equilibrium between the monomeric and dimeric form in solution, and, due to the low dimerization energy, as either monomers or dimers in the solid state, depending on the steric bulk of substituents. However, increasing the steric bulk of lead-bound substituents can prevent the close association of plumbylene molecules and allow the plumbylene to exist exclusively as monomers in solution or even in the solid state.
The driving force for dimerization in general arises from the Lewis amphoteric nature of plumbylenes, which possess a Lewis acidic vacant 6p orbital and a weakly Lewis basic 6s lone pair, which can act as electron acceptor and donor orbitals respectively.
These diplumbenes possess a "trans"-bent structure similar to that in lighter, non-carbon congeners (disilenes, digermylenes, distannylenes). The observed Pb–Pb bond lengths in diplumbenes (2.90 – 3.53 Å) have been found to typically be longer than those in tetravalent diplumbanes R3PbPbR3 (2.84 – 2.97 Å). This, together with the low computed dimerization energy (energy released from the formation of dimers from monomers) of 24 kJ mol−1 for Pb2H4, indicates weak multiple bonding. This counterintuitive result is due to the pair of 6s-6p donor-acceptor interactions representing the Pb=Pb double bond in diplumbenes being less energetically favourable compared to the overlap of spn orbitals (with a higher degree of hybridization than in diplumbenes) in the Pb–Pb single bond in diplumbanes.
In monohalogenated plumbylenes, the halogen atom on one plumbylene is able to donate a lone pair into the vacant 6p orbital of the lead atom on a separate plumbylene in a bridging mode. Monohalogenated plumbylenes have been found to generally exist as monomers in solution and dimers in the solid state, but, again, sufficiently bulky substituents on lead can sterically block this dimerization mode.
Due to decreasing dimerization energy down Group 14, while monohalogenated stannylenes and plumbylenes dimerize via the halogen-bridging mode, monohalogenated silylenes and germylenes tend to dimerize "via" the abovementioned multiply-bonded mode instead.
In a recent study, an "N"-heterocyclic plumbylene was shown to undergo dimerization leading to C–H activation, existing in solution in an equilibrium between the monomer and a dimer resulting from cleavage of an aryl C–H bond and formation of Pb–C and N–H bonds. DFT studies proposed that the reaction occurred via electrophilic substitution at the arene of one plumbylene by the lead atom of another, and involves concerted Pb–C and N–H bond formation instead of insertion of Pb into the C–H bond.
Stabilizing intramolecular interactions with substituents bearing lone pairs.
Plumbylenes may be stabilized by electron donation into the vacant orbital of the lead atom. The two common intramolecular modes are resonance from a lone pair on the atom directly attached to the lead or by coordination from a Lewis base elsewhere in the molecule.
For example, Group 15 or 16 elements directly adjacent to Pb donate a lone pair in manner similar to their stabilizing effect on Fisher carbenes. Common examples of more remote electron-donors include nitrogen atoms that can lead to a six-memberd ring by bonding to the lead. Even a fluorine atom on a remote trifluoromethyl group has been seen forming a coordination to lead in [2,4,6-(CF3)3C6H2]2Pb.
Agostic interactions.
Agostic interactions have also been shown to stabilize plumbylenes. DFT computations on the compounds [(R(CH3)2Si){(CH3)2P(BH3)}CH]2Pb (R = Me or Ph) found that agostic interactions between bonding B–H orbitals and the vacant 6p orbital lowered the energy of the molecule by "ca." 38 kcal mol−1; this was supported by X-ray crystal structures showing the favourable positioning of said B–H bonds in proximity of Pb.
Reactivity.
As previously mentioned, unstabilized plumbylenes are prone to polymerization and disproportionation, and plumbylenes without bulky substituents tend to dimerize in one of two modes. Below, the reactions of stabilized plumbylenes (at least at the temperatures at which they were studied) are listed.
Lewis acid-base adduct formation.
Plumbylenes are Lewis acidic "via" the vacant 6p orbital and tend to form adducts with Lewis bases, such as trimethylamine "N"-oxide (Me3NO), 1-azidoadamantane (AdN3), and mesityl azide (MesN3). In contrast, the reaction between stannylenes and Me3NO produces the corresponding distannoxane (from oxidation of Sn(II) to Sn(IV)) instead of the Lewis adduct, which can be attributed to tin being a period above Pb, experiencing the inert pair effect to a lesser degree and hence having a higher susceptibility to oxidation.
In the case of AdN3, the terminal N of the azidoadamantane binds to the plumbylene via a bridging mode between the Lewis acidic Pb and the Lewis basic P atom; in the case of MesN3, the azide evolves N2 to form a nitrene, which then inserts into a C-H bond of an arene substituent and coordinates to Pb as a Lewis base.
Insertion.
Similar to carbenes and other Group 14 congeners, plumbylenes have been shown to undergo insertion reactions, specifically into C–X (X = Br, I) and Group 16 E–E (E = S, Se) bonds.
Insertions into lead-substituent bonds can also occur.27 In the examples below, insertion is accompanied by intramolecular rearrangement to place more electron-donating heteroatoms next to the electron-deficient lead.27
Transmetallation.
Plumbylenes are known to undergo nucleophilic substitution with organometallic reagents to form transmetallated products.28 In an unusual example, the use of TlPF6, bearing the weakly coordinating anion PF6−, led to the formation of crystals of an oligonuclear lead compound with a chain structure upon work-up, highlighting the interesting reactivity of plumbylenes.28
In addition, plumbylenes can also undergo metathesis with group 13 E(CH3)3 (E = Al, Ga) compounds.
Plumbylenes bearing different substituents can also undergo transmetallation and exchange substituents, with the driving force being the relief of steric strain and the low Pb-C bond dissociation energy.
Applications.
Plumbylenes can be used as concurrent σ-donor-σ-acceptor ligands to metal complexes, functioning as σ-donor via its filled 6s orbital and σ-acceptor via its empty 6p orbital.
Room temperature-stable plumbylenes have also been suggested as precursors in chemical vapour deposition (CVD) and atomic layer deposition (ALD) of lead-containing materials. Dithioplumbylenes and dialkoxyplumbylenes may be useful as precursors for preparing the semiconductor material lead sulphide and piezoelectric PZT respectively.


Goslarite

Goslarite is a hydrated zinc sulfate mineral (ZnSO4) which was first found in the Rammelsberg mine, Goslar, Harz, Germany. It was described in 1847. Goslarite belongs to the epsomite group which also includes epsomite (MgSO4) and morenosite (NiSO4). Goslarite is an unstable mineral at the surface and will dehydrate to other minerals like bianchite (ZnSO4), boyleite (ZnSO4) and gunningite (ZnSO4).
Physical properties.
The composition of goslarite was determined by the US National Bureau of Standards (now the National Institute of Standards and Technology) in 1959 as follows: SO3 27.84 wt%, ZnO 28.30 wt% and 43.86 wt%.
Goslarite's cleavage is perfect in {010}, as for epsomite and morenosite. The color of goslarite ranges from brownish to pinkish, blue, brown, colorless, green and green blue. The luster ranges from vitreous to nacreous and silky (if fibrous). Goslarite is soluble in water, has an astringent taste, and is strongly diamagnetic.
Geologic occurrence.
Goslarite is formed from the oxidation of sphalerite ((Zn, Fe)S). It was first found in Rammelsberg mine, Goslar, Harz, Germany. It often occurs as an efflorescence on timbers and walls of mine passages. Goslarite is widespread as a post mining efflorescence in mines that contain sphalerite or any zinc minerals.
Economical uses.
In the pharmaceutical industry it is used as a direct emetic, antiseptic and disinfectant.


Borylation

Metal-catalyzed C–H borylation reactions are transition metal catalyzed organic reactions that produce an organoboron compound through functionalization of aliphatic and aromatic C–H bonds and are therefore useful reactions for carbon–hydrogen bond activation. Metal-catalyzed C–H borylation reactions utilize transition metals to directly convert a C–H bond into a C–B bond. This route can be advantageous compared to traditional borylation reactions by making use of cheap and abundant hydrocarbon starting material, limiting prefunctionalized organic compounds, reducing toxic byproducts, and streamlining the synthesis of biologically important molecules. Boronic acids, and boronic esters are common boryl groups incorporated into organic molecules through borylation reactions. Boronic acids are trivalent boron-containing organic compounds that possess one alkyl substituent and two hydroxyl groups. Similarly, boronic esters possess one alkyl substituent and two ester groups. Boronic acids and esters are classified depending on the type of carbon group (R) directly bonded to boron, for example alkyl-, alkenyl-, alkynyl-, and aryl-boronic esters. The most common type of starting materials that incorporate boronic esters into organic compounds for transition metal catalyzed borylation reactions have the general formula (RO)2B-B(OR)2. For example, bis(pinacolato)diboron (B2Pin2), and bis(catecholato)diborane (B2Cat2) are common boron sources of this general formula.
The boron atom of a boronic ester or acid is sp2 hybridized possessing a vacant p orbital, enabling these groups to act as Lewis acids. The C–B bond of boronic acids and esters are slightly longer than typical C–C single bonds with a range of 1.55-1.59 Å. The lengthened C–B bond relative to the C–C bond results in a bond energy that is also slightly less than that of C–C bonds (323 kJ/mol for C–B vs 358 kJ/mol for C–C). The carbon–hydrogen bond has a bond length of about 1.09 Å, and a bond energy of about 413 kJ/mol. The C–B bond is therefore a useful intermediate as a bond that replaces a typically unreactive C–H bond.
Organoboron compounds are organic compounds containing a carbon-boron bond. Organoboron compounds have broad applications for chemical synthesis because the C–B bond can easily be converted into a C–X (X = Br, Cl), C–O, C–N, or C–C bond. Because of the versatility of the C–B bond numerous processes have been developed to incorporate them into organic compounds. Organoboron compounds are traditionally synthesized from Grignard reagents through hydroboration, or diboration reactions. Borylation provides an alternative.
Metal-catalyzed C–H borylation reactions.
Aliphatic C–H borylation.
As first described by Hartwig, alkanes can be selectively borylated with high selectivity for the primary C–H bond using Cp*Rh(η4-C6Me6) as the catalyst. Notably, selectivity for the primary C–H bond is exclusive even in the presence of heteroatoms in the carbon-hydrogen chain. The rhodium-catalyzed borylation of methyl C–H bonds occurs selectively without a dependence on the position of the heteroatom. Borylation occurs selectively at the least sterically hindered and least electron rich primary C–H bond in a range of acetals, ethers, amines, and alkyl fluorides. Additionally, no reaction is shown to occur in the absence of primary C–H bonds, for example when cyclohexane is the substrate.
Selective functionalization of a primary alkane bond is due to the formation of a kinetically and thermodynamically favorable primary alkyl-metal complex over formation of a secondary alkyl-metal complex.
The greater stability of primary versus secondary alkyl complexes can be attributed to several factors. First, the primary alkyl complex is favored sterically over the secondary alkyl complex. Second, partial negative charges are often present on the α-carbon of a metal-alkyl complex and a primary alkyl ligand supports a partial negative charge better than a secondary alkyl ligand.
The origin of selectivity for aliphatic C–H borylation using rhodium catalysts was probed using a type of mechanistic study called hydrogen–deuterium exchange. H/D exchanged showed that regioselectivity of the overall process shown below results from selective cleavage of primary over secondary C–H bonds and selective functionalization of the primary metal-alkyl intermediate over the secondary metal-alkyl intermediate.
The synthetic utility of aliphatic C–H borylation has been applied to the modification of polymers through borylation followed by oxidation to form hydroxyl-functionalized polymers.
Aromatic C–H borylation.
Steric directed C–H borylation of arenes.
The first example of a catalytic C–H borylation of an unactivated hydrocarbon (benzene) was reported by Smith and Iverson using Ir(Cp*)(H)(Bpin) as the catalyst. The efficiency of this system, however, was low, providing only 3 turnovers after 120 h at 150 °C. Numerous subsequent developments by Hartwig and coworkers led to efficient, practical conditions for arene borylation. Aromatic C–H borylation was developed by Hartwig and Ishiyama using the diboron reagent Bis(pinacolato)diboron catalyzed by 4,4’-di-tert-butylbipyridine (dtbpy) and [Ir(COD)(OMe)]2. With this catalyst system the borylation of aromatic C–H bonds occurs with regioselectivity that is controlled by steric effects of the starting arene. The selectivity for functionalization of aromatic C–H bonds is governed by the general rule that the reaction does not occur "ortho" to a substituent when a C–H bond lacking an "ortho" substituent is available. When only one functional group is present borylation occurs in the meta and para position in statistical ratios of 2:1 (meta:para). The "ortho" isomer is not detected due to the steric effects of the substituent.
Addition of Bpin occurs in only one position for symmetrically substituted 1,2- and 1,4-substituted arenes. Symmetrical or unsymmetrical 1,3-substituted arenes are also selectively borylated because only one C–H bond is sterically accessible.
This is in contrast to Electrophilic aromatic substitution where regioselectivity is governed by electronic effects.
The synthetic importance of aromatic C–H borylation is shown below, where a 1,3-disubstited aromatic compound can be directly converted to a 1,3,5-organoborane compound and subsequently functionalized.
Aromatic C–H functionalization was successfully incorporated in the total synthesis of Complanadine A, a "Lycopodium" alkaloid that enhances mRNA expression for nerve growth factor (NGF) and the production of NGF in human glial cells. Natural products that promote the growth of new neural networks are of interest in the treatment of diseases such as Alzheimer's disease. Complanadine A was successfully synthesized using a combination of direct aromatic C–H borylation developed by Hartwig and Ishyiama, followed by Suzuki–Miyaura cross coupling, then cleavage of the Boc protecting group.
C–H borylation of heteroarenes.
Heteroarenes can also undergo borylation under iridium-catalyzed conditions, however, site-selectivity in this case is controlled by electronic effects, where furans, pyrroles, and thiophenes undergo reaction at the C–H bond alpha to the heteroatom. In this case selectivity is suggested to occur through the C–H bond alpha to the heteroatom because it is the most acidic C–H bond and therefore the most reactive.
Directed "ortho" C–H borylation.
Using the same catalyst system directing groups can be employed to achieve regioselectivity without substituents as steric mediators. For example, Boebel and Hartwig reported a method to conduct "ortho"-borylation where a dimethyl-hydrosilyl directing group on the arene undergoes iridium catalyzed borylation at the C–H bond "ortho" to the silane directing group. Selectivity for the "ortho" position in the case of using hydrosilyl directing groups has been attributed to reversible addition of the Si-H bond to the metal center, leading to preferential cleavage of the C–H bond "ortho" to the hydrosilyl substituent. Several other strategies to achieve "ortho"-borylation of arenes have been developed using various directing groups.
Mechanistic detail for the C–H borlyation of arenes.
A trisboryl iridium complex has been proposed to facilitate the mechanism for each of these reactions that result in C–H borylation of arenes and heteroarenes. Kinetic studies and isotopic labelling studies have revealed that an Ir(III) triboryl complex reacts with the arene in the catalytic process.
A version of the catalytic cycle is shown below for the "ortho" borylation of hydrosilane compounds. Kinetic data show that an observed trisboryl complex coordinated to cyclooctene rapidly and reversibly dissociates cyclooctene to form a 16 electron trisboryl complex. In the case of using benzyldimethylsilane as a directing group it is proposed that benzyldimethylsilane reacts with the trisboryl iridium catalyst through reversible addition of the Si-H bond to the metal center, followed by selective "ortho"-C–H bond activation via oxidative addition and reductive elimination.
Meta-Selective Borylation: Meta-Selective C–H borylation is an important synthetic transformation, which was discovered in 2002 by Smith III from Michigan State University, USA. However, this meta borylation was completely sterically directed and was limitted to only 1,3-disubstituted benzenes. Around 12 years later, Dr. Chattopadhyay and his team from Centre of Biomedical Research, U.P, India discovered an elegant technology for the meta-selective C–H bond activation and borylation. The team had shown that using the same substrate, one can switch the other positional selectivity just changing the ligand. The origin of the meta-selectivity was defined by the two parameter, such as: 1) electrostatic interaction, 2) a secondary B-N interaction.
At the same time, a team from Japan, Dr. Kanai reported an amazing concept for the meta-selective borylation based on the secondary interaction. This method covers various carbonyl compounds borylation.
Reduction reactions with organoboron compounds.
Corey–Bakshi–Shibata reduction (CBS reduction).
In 1981, Hirao and co-workers have found that asymmetric reduction of prochiral aromatic ketones with chiral amino alcohols and borane afforded the corresponding secondary alcohols with 60% ee. They found out that the chiral amino alcohols would react with borane to form aloxyl-amine-borane complexes. The complexes are proposed to contain a relatively rigid five member-ring system which makes them thermal and hydrolytic stable and soluble in a wide variety of protic and aprotic solvents.
In 1987, E. J. Corey and co-workers found out that the formation of oxazaborolidines from borane and chiral amino alcohols. And the oxazaborolidines were found to catalyze the rapid and highly enantioselective reduction of prochiral ketones in the presence of BH3THF. This enantioselective reduction of achiral ketones with catalytic oxazaborolidine is called Corey–Bakshi–Shibata reduction or CBS reduction.
Midland Alpine-borane reduction (Midland reduction).
In 1977, M. M. Midland and co-workers reported a surprising observation that B-3-alpha-Pinanyl-9-borabicyclo [3,3,1] nonane, readily prepared by hydroboration of (+)-alpha-pinene with 9-borobicyclo[3,3,1] nonane, rapidly reduces benzaldehyde-alpha-d to (S)-(+)-benzyl-alpha-d alcohol with an essentially quantitative asymmetric induction.
In the same year, M. M. Midland discovered B-3-alpha-pinanyl-9-BBN as the reducing agent, which could be easily available by reacting (+)-alpha-pinene with 9-BBN. The new reducing agent was later commercialized by Aldrich Co. under the name Alpine Borane and the asymmetric reduction of carbonyl groups with either enantiomer of Alpine-Borane is known as Midland Alpine-Borane reduction.
In 2012, U. R. Y. Venkateswarlu and co-workers have reported a stereoselective method to synthesize pectinolide H. Midland reduction and Sharpless dihydroxylation reaction are involved in generating the three chiral centers at C–4’, C–5 and C–1’.
Coupling reactions with organoboron compounds.
Petasis boronic acid-Mannich reaction.
In 1993, N. A. Petasis and I. Akrltopoulou reported an efficient synthesis of allylic amines with a modified Mannich reaction. In this modified Mannich reaction, they have found that vinyl boronic acids can participate as nucleophiles to give geometrically pure allylamines. This modified Mannich reaction was known as Petasis boronic acid-Mannich Reaction.
Roush asymmetric allylation.
In 1978, R. W. Hoffmann and T. Herold reported on the enantioselective synthesis of secondary homoallyl alcohols via chiral non-racemic allylboronic esters. The homoallylic alcohols were formed with excellent yield and moderate enantioselectivity.
In 1985, W. R. Roush and co-workers found out that tartrate modified allylic boronates offer a simple, highly attractive approach to the control of facial selectivity in reactions with chiral and achiral aldehydes. In the following years, W.R. Roush and co-workers extended this strategy to the synthesis of 2-butene-1,4-diols and anti-diols. This kind of reaction is known as Rouch asymmetric allylation.
In 2011, R. A. Fernandes and P. Kattanguru have completed an improved total synthesis of (8S, 11R, 12R)- and (8R, 11R, 12R)-topsentolide B2 diastereomers in eight steps. In the paper, diastereoselective Roush allylation reaction was used as a key reaction in the total synthesis to introduce two chiral intermediate. And then the authors synthesized the two diastereomers through these two chiral intermediates.
Suzuki–Miyaura cross-coupling.
In 1979, N. Miyaura and A. Suzuki reported the synthesis of arylated (E)-alkenes in high yield from aryl halides with alkyl-1-enylboranes and catalyzed by tetrakis(triphenylphosphine)palladium and bases. Then A. Suzuki and co-workers extend this kind of reaction to other organoboron compounds and other alkenyl, aryl, alkyl halides and triflate. The palladium-catalyzed cross-coupling reaction organoboron compounds and these organic halides to form carbon-carbon bonds are known as Suzuki–Miyaura Cross-Coupling.
In 2013, Joachim Podlech and co-workers determined the structure of Alternaria mycotoxin altenuic acid III by NMR spectroscopic analysis and completed its total synthesis. In the synthetic strategy, Suzuki-Miyaura Cross-Coupling reaction was used with a highly functionalized boronate and butenolides to synthesize a precursor of the natural product in high yield.
Modified Ullmann biaryl ether and biaryl amine synthesis.
In 1904, Fritz Ullmann found out that copper powder could significantly improve the reaction of aryl halides with phenols to give biaryl ethers. This reaction is known as Ullmann condensation. In 1906, I. Goldberg extended this reaction to synthesize an arylamine by reacting aryl halides with an amide in the presence of Potassium Carbonate and CuI. This reaction is known as Goldberg modified Ullmann condensation. In 2003, R. A. Batey and T. D. Quach have modified this kind of reactions by using potassium organotrifluoroborates salts to react with aliphatic alcohols, aliphatic amines or anilines to synthesize aryl ethers or aryl amines.


Unpentpentium


Silylation

Silylation is the introduction of a (usually) substituted silyl group (R3Si) to a molecule. The process is the basis of organosilicon chemistry.
Of organic compounds.
Alcohols, carboxylic acids, amines, thiols, and phosphates can be silylated. The process involves the replacement of a proton with a trialkylsilyl group, typically trimethylsilyl (-SiMe3). Generally the substrate is deprotonated with a suitable strong base followed by treatment with a silyl chloride (e.g. trimethylsilyl chloride). Often strong bases such butyl lithium or a Grignard reagent are used, as illustrated by the synthesis of a trimethylsilyl ethers as protecting groups from an alcohol:
Bis(trimethylsilyl)acetamide ("BSA", Me3SiNC(OSiMe3)Me is an efficient silylation agent used for the derivatisation of compounds. The reaction of BSA with alcohols gives the corresponding trimethylsilyl ether, together with N-(trimethylsilyl)acetamide as a byproduct:
The introduction of a silyl group(s) gives derivatives of enhanced volatility, making the derivatives suitable for analysis by gas chromatography and electron-impact mass spectrometry (EI-MS). For EI-MS, the silyl derivatives give more favorable diagnostic fragmentation patterns of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.
Desilylation.
Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluoride salts (e.g. sodium, potassium, tetra-n-butylammonium fluorides) are popular for this purpose.
Of metals.
Coordination complexes with silyl ligands are well known. An early example is CpFe(CO)2Si(CH3)3, prepared by a salt metathesis reaction from trimethylsilyl chloride and CpFe(CO)2Na. Typical routes include oxidative addition of Si-H bonds to low-valent metals. Metal silyl complexes are intermediates in hydrosilation, a process used to make organosilicon compounds on both laboratory and commercial scales.


Umohoite

Umohoite is a rare oxide and hydroxide mineral. The name of this mineral reflects its composition: uranyl (U), molybdate (Mo) and water (H2O). Its chemical formula is (UO2)MoO4·2H2O.
Umohoide's type location is in Marysvale, the mineral was first described by Paul F. Kerr and G. P. Brophy in 1953.


Tetramethyllead

Tetramethyllead, also called tetra methyllead and lead tetramethyl, is a chemical compound used as an antiknock additive for gasoline. Its use is being phased out for environmental considerations.
The National Institute for Occupational Safety and Health (NIOSH) in the United States has identified tetramethyllead as a potential workplace hazard. The recommended time-weighted average exposure limit to tetramethyllead is 0.075 milligrams per cubic meter during a 10-hour workday; the OSHA permissible exposure limit is the same value assuming an 8-hour workday.
Exposure to tetramethyllead can affect the central nervous system, the kidneys, and the cardiovascular system. Tetramethyllead can be absorbed through inhalation, through eye contact, through skin absorption, and by ingesting the substance. Symptoms of exposure include insomnia, coma, seizure, mania, delirium, loss of appetite, nausea, hypotension, anxiety, restlessness, and nightmares. First aid measures for exposure include artificial respiration, immediate eye irrigation, and immediate washing with water. Immediate medical attention should be sought if tetramethyllead is ingested.


Tantalum(V) ethoxide

Tantalum(V) ethoxide is a metalorganic compound with formula Ta2(OC2H5)10, often abbreviated as Ta2(OEt)10. It is a colorless solid that dissolves in some organic solvents but hydrolyzes readily. It is used to prepare films of tantalum(V) oxide.
Structure.
Tantalum(V) alkoxides typically exist as dimers with octahedral six-coordinate tantalum metal centres. Subsequent crystallographic analysis established that the methoxide and isopropoxides of niobium adopt bioctahedral structures. From a geometric perspective, the ten ethoxide ligand oxygen atoms of the Ta2(OEt)10 molecule in solution define a pair of octahedra sharing a common edge with the two tantalum atoms located at their centres. From a bonding perspective, each tantalum centre is surrounded octahedrally by four monodentate and two bridging ethoxide ligands. The oxygen atoms of the bridging ethoxides are each bonded to both tantalum centres, and these two ligands are "cis" to one another within the coordination sphere. The formula [(EtO)4Ta(μ-OEt)]2 more comprehensively represents this dimeric structure, although the simplified formula is commonly used for most purposes.
Preparation.
Several approaches are known for preparing tantalum(V) ethoxide. Salt metathesis from tantalum(V) chloride is generally the most successful. Tantalum pentachloride, Ta2Cl10, provides a convenient starting point. To avoid the generation of mixed chloride-ethoxide species, a base such as ammonia is usually added to trap liberated HCl:
Salt metathesis using an alkali metal alkoxide can be used as well:
The same compound can be prepared electrochemically. The two half-equations and the overall equation for this reaction are:
Commercial production of tantalum(V) ethoxide using this electrochemical approach has been employed in Russia. The compound can also be prepared by direct reaction of tantalum metal with ethanol, in which case the overall equation is the same as that shown above for the electrochemical approach.
Since the 1970’s, Bayer of Germany had been producing tantalum (V) ethoxide in Leverkusen, however following the break-up of Bayer, production moved to Heraeus.
Meanwhile, Inorgtech (later MultiValent), started production in 1974 in Cambridge, UK.
Both routes involved the direct reaction of the metal chloride with alcohol in the presence of solvents to give a product of 99.999%+ purity.
Reactions.
The most important reaction of tantalum alkoxides is hydrolysis to produce films and gels of tantalum oxides. Although these reactions are complex, the formation of a tantalum(V) oxide film by hydrolysis can be described by this simplified equation:
Tantalum(V) ethoxide optical coatings can be produced by low pressure chemical vapour deposition. At pressures as low as 1.33 mPa and temperatures of 700 °C, a silica film of the desired depth is first deposited by the decomposition of tetraethoxysilane, Si(OEt)4, or di-"t"-butyoxydiacetoxysilane, Si(OC(CH3)3)2(OOCCH3)2, then tantalum(V) ethoxide is introduced. As in the case of niobium(V) ethoxide, the ethoxide precursor thermally decomposes to produce the oxide layer with the associated release of diethyl ether:
Pyrolysis also produces a tantalum(V) oxide film by chemical vapor deposition in which case the tantalum(V) ethoxide is completely oxidised, producing carbon dioxide and water vapor:
Amorphous tantalum(V) oxide films can also be prepared by atomic layer deposition or by a pulsed chemical vapour deposition technique in which tantalum(V) ethoxide and tantalum(V) chloride are applied alternately. At temperatures approaching 450 °C the films produced have refractive indices and permittivity properties similar to those produced from conventional approaches. The preparation of these films occurs with the loss of chloroethane:
Sol-gel processing also produces thin films of tantalum(V) oxide using a similar chemical approach. Sol-gel routes using tantalum(V) ethoxide to generate layered perovskite materials have also been developed.
Applications.
It is mainly used for the manufacture of tantalum(V) oxide thin-film materials by approaches including chemical vapor deposition, atomic layer deposition, and sol-gel processing. These materials have semiconductor, electrochromic, and optical applications.
Tantalum(V) oxide films have a variety of applications including as optical films with refractive indices as high as 2.039 and as a thin-film dielectric material in dynamic random access memory and semiconductor field-effect transistors. The approach chosen for preparation of these materials is determined by the desired properties. Direct hydrolysis is appropriate when the presence of residual water or the use of high temperatures for drying is acceptable. Micropatterns can be produced by site-selective deposition using the hydrolysis approach by forming a self-assembled monolayer followed by high temperature annealling. Chemical vapour deposition allows control of the thickness of the film on a nanometre scale, which is essential for some applications. Direct pyrolysis is convenient for optical applications, where transparent materials with low light loss due to absorption is important, and has also been used to prepare nitride read-only memory. Electrochromism is the property of some materials to change color when charge is applied, and is the means by which so-called smart glass operates. Films produced by tantalum(V) ethoxide hydrolysis has been used to prepare amorphous tantalum(V) oxide films suitable for electrochromic applications.
Mixed-metal thin-films have also been prepared from this compound. For example, lithium tantalate, LiTaO3, films are desirable for their non-linear optical properties and have been prepared by first reacting tantalum(V) ethoxide with lithium dipivaloylmethanate, LiCH(COC(CH3)3)2, to prepare a precursor suitable for metalorganic vapour phase epitaxy (a form of chemical vapor deposition). Films of strontium tantalate, Sr(TaO3)2, have also been prepared using atomic layer deposition approaches and their properties investigated.
Tantalum(V) ethoxide condenses with carboxylic acids to give oxo-alkoxide-carboxylates, e.g., Ta4O4(OEt)8(OOCCH3)4. The Ta4O4 core of such compounds form a cubane-type cluster.


Manganese(II) nitrate

Manganese(II) nitrate are the inorganic salts with formula Mn(NO3)2·(H2O)n. Each formula unit is composed of one Mn2+ cation and two NO3− anions and varying amounts of water. Most common is the tetrahydrate Mn(NO3)2·4H2O, but mono- and hexahydrates are also known as well as the anhydrous compound. Some of these compounds are useful precursors to the oxides of manganese.
Preparation, reactions, uses.
Manganese(II) nitrate is prepared by dissolving manganese(II) oxide in nitric acid:
It can also be prepared from manganese dioxide and nitrogen dioxide:
On heating to 300 °C, aqueous solutions of manganese(II) nitrate thermally decompose to form MnO2 and NO2.
Manganese(II) nitrate is the precursor to manganese carbonate, which is used in fertilizers and as a colorant. The advantage of this method, use of ammonia and carbon dioxide, being that the side product ammonium nitrate is also useful as a fertilizer.


Selective chemistry of single-walled nanotubes

Selective chemistry of single-walled nanotubes is a field in Carbon nanotube chemistry devoted specifically to the study of functionalization of single-walled carbon nanotubes.
Structure and reactivity.
Reactivity of fullerene molecules with respect to addition chemistries is strongly dependent on the curvature of the carbon framework. Their outer surface (exohedral) reactivity increases with increase in curvature. In comparison with fullerene molecules single-walled nanotubes (SWNTs) are moderately curved. Consequently, nanotubes are expected to be less reactive than most fullerene molecules due to their smaller curvature, but more reactive than a graphene sheet due to pyramidalization and misalignment of pi-orbitals. The strain of a carbon framework is also reflected in the pyramidalization angle (Өp) of the carbon constituents. Trigonal carbon atoms (sp2 hybridized) prefer a planar orientation with Өp=0° (i.e. graphene) and fullerene molecules have Өp= 11.6°. The (5,5) SWNT has Өp~6° for the sidewall. Values for other (n,n) nanotubes show a trend of increasing Өp (sidewall) with decrease in n. Therefore, generally the chemical reactivity of SWNT increases with decrease in diameter (or n, diameter increases with n). Apart from the curvature SWNT reactivity is also highly sensitive to chiral wrapping (n,m) which determine its electronic structure. Nanotubes with "n - m = 3i" ("i" is an integer) are all metals and rest are all semiconducting (SC).
Sidewall functionalization.
Carbon nanotubes are metallic or semiconducting, based upon delocalized electrons occupying a 1-D density of states. However, any covalent bond on SWNT sidewall causes localization of these electrons. In the vicinity of localized electrons, the SWNT can no longer be described using a band model that assumes delocalized electrons moving in a periodic potential.
Two important addition reactions of SWNT sidewall are: (1) Fluorination, and (2) Aryl diazonium salt addition. These functional groups on SWNT improve solubility and processibility. Moreover, these reactions allow for combining unique properties of SWNTs with those of other compounds. Above all, the selective diazonium chemistry can be used to separate the semiconducting and metallic nanotubes.
Fluorination.
The first extensive SWNT sidewall reaction was fluorination in 1998 by Mickleson et al. These fluorine moieties can be removed from the nanotube by treatment in hydrazine and the spectroscopic properties of the SWNT can be restored completely.
Diazonium chemistry.
One of the most important SWNT sidewall reaction is that with diazonium reagent which if done under controlled conditions can be used to do selective covalent chemistry.
Water-soluble diazonium salts react with carbon nanotubes via charge transfer in which they extract electrons from SWNT and form a stable covalent aryl bond. This covalent aryl bond forms with extremely high affinity for electrons with energies near the Fermi level, Ef of the nanotube. Metallic SWNT have a greater electron density near Ef resulting in their higher reactivity over semiconducting nanotubes. The reactant forms a charge-transfer complex at the nanotube surface, where electron donation from the latter stabilizes the transition state and accelerates the forward rate. Once the bond symmetry of the nanotube is disrupted by the formation of this defect, adjacent carbons increase in reactivity and initial selectivity for metallic SWNT is amplified. Under carefully controlled conditions this behavior can be exploited to obtain highly selective functionalization of metallic nanotubes to the near exclusion of the semiconductors.
Selective reaction conditions.
Primary condition is addition of reactant molecules at a very small rate to SWNT solution for a sufficient long time. This ensures reaction with only metallic SWNTs and with no semiconducting SWNTs as all the reactant molecules are taken up by the metallic SWNTs. Long time injection ensures that all metallic tubes are reacted. For example, one highly selective condition is: addition of 500 µL of 4-hydroxybenzene diazonium tetrafluoroborate solution in water (0.245 mM) at an injection rate of 20.83 µL/h into 5 mL of SWNT solution (1 wt % sodium dodecyl sulfate (SDS)) over 24 hrs. However, if the entire diazonium solution is added all instantaneously then semiconducting SWNTs will also react due to presence of excess reactant.
Spectroscopy and functionalization.
SWNTs have unique optical and spectroscopic properties largely due to one-dimensional confinement of electronic and phonon states, resulting in so-called van Hove singularities in the nanotube density of states (DOS).
Probing selective chemistry via optical absorption.
Optical absorption monitors the valence (v) to conduction (c) electronic transitions denoted Enn where n is the band index. The E11 transitions for the metallic nanotubes occur from ~440 to 645 nm. The E11 and E22 transitions for the semiconducting nanotubes are found from 830 to 1600 nm and 600 to 800 nm, respectively. These separated absorption features allow for the monitoring of valence electrons in each distinct nanotube. Reaction at the surface result in localization of valence electrons makes them no longer free to participate in photoabsorption which results in decay of the spectrum features.
Selective diazonium chemistry abruptly decreases the peak intensities that represent the first Van Hove transition of metallic species (E11, metal), while the peak intensities representing the second (E22, semiconducting) and first (E11, semiconducting) Van Hove transition of the semiconducting species show little or no change. A relative decrease in metallic SWNT absorption features over semiconducting features represents a highly preferential functionalization of the metallic nanotubes.
Raman spectroscopy.
Raman spectroscopy is a powerful technique with wide-ranging applications in carbon nanotube studies. Some important Raman features are radial breathing mode (RBM), tangential mode (G-band), and disorder-related mode.
RBM features correspond to the coherent vibration of the C atoms in the radial direction of the nanotube. These features are unique in carbon nanotubes and occur with the frequencies ωRBM between 120 and 350 cm−1 for SWNT in the diameter range (0.7 nm-2 nm). They can be used to probe the SWNT diameter, electronic structure through their frequency and intensity (IRBM) respectively and hence perform an (n,m) assignment to their peaks. The addition of the moiety to the sidewall of the nanotube disrupts the oscillator strength that gives rise to RBM feature and hence causes decay of these features. These features are distinct for species of a particular nanotube (n,m) and hence enables to probe which SWNTs are functionalized and to what extent.
Two main components of the tangential mode include G+ at 1590 cm−1 and G− at 1570 cm−1. G+ feature is associated with carbon atom vibrations along the nanotube axis. The G− feature is associated with vibrations of carbon atoms along the circumferential direction. The G-band frequency can be used (1) to distinguish between metallic and semiconducting SWNTs, and (2) to probe charge transfer arising from doping a SWNT. Frequency of G+ is sensitive to charge transfer. It upshifts for acceptors and downshifts for donors. Lineshape of G− is highly sensitive to whether SWNT is metallic (Breit-Wigner-Fano lineshape) or semiconducting (Lorentzian lineshape).
The disorder-related mode (D peak) is a phonon mode at 1300 cm−1 and involves the resonantly enhanced scattering of an electron via phonon emission by a defect that breaks the basic symmetry of the graphene plane. This mode corresponds to the conversion of a sp2-hybridized carbon to a sp3-hybridized on the surface. Intensity of D peak measures covalent bond made with the nanotube surface. This feature does not increase as a result of surfactant or hydronium ion adsorption on the nanotube surface.
Selective reaction and Raman features.
Selective functionalization increases the intensity of the D peak due to formation of aryl-nanotube bond and decreases the tangential mode due loss of electronic resonance. These two effects are generally summed together as increase in their peaks ratio (D/G). RBM peaks of metallic nanotubes decay and the peaks corresponding to those of semiconducting nanotubes remain almost unchanged.
Reaction mechanism.
Diazonium reagent and SWNT reaction has a two step mechanism. First, the diazonium reagent adsorbs noncovalently to an empty site on the nanotube surface, forming a charge-transfer complex. This is a fast, selective noncovalent adsorption and diazonium group in this complex partially dopes the nanotube, diminishing the tangential mode in the Raman spectrum. Desorption of A from nanotube is negligible (k−1 ~ 0). In second step complex B then decomposes to form a covalent bond with the nanotube surface. This is a slower step that need not be selective and is represented by the restoration of the G peak and increase in the D band.
Reversibility of diazonium chemistry.
Nanotubes reacted with the diazonium reagent can be converted back into pristine nanotubes when thermally treated at 300 °C in an atmosphere of inert gas. This cleaves the aryl hydroxyl moieties from the nanotube sidewall and restores the spectroscopic feature (Raman and absorption spectra) of pristine nanotube.
Chemical separation of metallic and semiconducting SWNTs.
Metallic and semiconducting carbon nanotubes generally coexist in as-grown materials. To get only semiconducting or only metallic nanotubes selective functionalization of metallic SWNTs via 4-hydroxybenzene diazonium can be used. Separation can be done in solution by deprotonation of the p-hydroxybenzene group on the reacted nanotubes (metallic) in alkaline solution followed by electrophoretic separation of these charged species from the neutral species (semiconducting nanotubes). This followed by annealing would give separated pristine semiconducting and metallic SWNT.


Sulfurous acid

Sulfurous acid (also Sulfuric(IV) acid, Sulphuric acid (UK), Sulphuric(IV) acid (UK)) is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogen sulfite) and sulfite. Sulfurous acid is an intermediate species in the formation of acid rain from sulfur dioxide.
Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO2 molecule and the bisulfite ion, . The intensities of the signals are consistent with the following equilibrium:
17O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium:
When trying to concentrate the solution by evaporation to produce waterless sulfurous acid it will decompose (reversing the forming reaction). In cooling down a clathrate SO2·H2O will crystallise which decomposes again at 7 °C. Thus sulfurous acid H2SO3 cannot be isolated.
Uses.
Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid, are used as reducing agents and as disinfectants, as are solutions of bisulfite and sulfite salts. They are oxidised to sulfuric acid or sulfate by accepting another oxygen atom.


Rammelsbergite

Rammelsbergite is a nickel arsenide mineral with formula NiAs2. It forms metallic silvery to tin white to reddish orthorhombic prismatic crystals, and is usually massive in form. It has a Mohs hardness of 5.5 and a specific gravity of 7.1.
It was first described in 1854 from its type locality in the Schneeberg District in Saxony, Germany. It was named after the German chemist and mineralogist, Karl Friedrich August Rammelsberg (1813–1899).
It occurs as a hydrothermal mineral in medium temperature veins association with skutterudite, safflorite, lollingite, nickeline, native bismuth, native silver, algodonite, domeykite and uraninite.


Thionyl group

The thionyl group is SO, a sulfur atom plus an oxygen atom.
It occurs in compounds such as thionyl fluoride, SOF2.
Thionyl chloride, SOCl2, is a common reagent used in organic synthesis to convert carboxylic acids to acyl chlorides.
In organic chemistry, the thionyl group is known as a sulfoxide group or sulfinyl group, and has the general structure RS(=O)R'.


Anglesite

Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and celestine. It contains 74% of lead by mass and therefore has a high specific gravity of 6.3. Anglesite's color is white or gray with pale yellow streaks. It may be dark gray if impure.
It was first recognized as a mineral species by William Withering in 1783, who discovered it in the Parys copper-mine in Anglesey; the name anglesite, from this locality, was given by F. S. Beudant in 1832. The crystals from Anglesey, which were formerly found abundantly on a matrix of dull limonite, are small in size and simple in form, being usually bounded by four faces of a prism and four faces of a dome; they are brownish-yellow in colour owing to a stain of limonite. Crystals from some other localities, notably from in Sardinia, are transparent and colourless, possessed of a brilliant adamantine lustre, and usually modified by numerous bright faces. The variety of combinations and habits presented by the crystals is very extensive, nearly two hundred distinct forms being figured by V. von Lang in his monograph of the species; without measurement of the angles the crystals are frequently difficult to decipher. There are distinct cleavages parallel to the faces of the prism (110) and the basal plane (001), but these are not so well developed as in the isomorphous minerals barite and celestite.
Anglesite is a mineral of secondary origin, having been formed by the oxidation of galena in the upper parts of mineral lodes where these have been affected by weathering processes. At Monteponi the crystals encrust cavities in glistening granular galena; and from Leadhills, in Scotland, pseudomorphs of anglesite after galena are known. At most localities it is found as isolated crystals in the lead-bearing lodes, but at some places, in Australia and Mexico, it occurs as large masses, and is then mined as an ore of lead.
Anglesite is sometimes used as a gemstone.
See also.
Lead(II) sulfate


Inesite

Inesite is a hydrous calcium manganese silicate mineral.  Its chemical formula is Ca2Mn7Si10O28(OH)2•5(H2O). Inesite is an inosilicate with a triclinic crystal system. It has a Mohs hardness of 5.5 to 6, and a specific gravity of 3.0. Its name originates from the Greek Ίνες (), "fibers" in allusion to its color and habit.
Occurrence and distribution.
Inesite occurs in hydrothermal replacement deposits of manganese-rich metamorphic rocks and serpentines.  It was first described in 1887 at Hilfe Gottes Mine, Oberscheld, Dillenburg, Dillenburg District, Hesse, Germany. Outside of the type locality, there are several notable localities of inesite, such as:


Silver oxalate

Silver oxalate () is commonly employed in experimental petrology to add carbon dioxide () to experiments as it will break down to silver (Ag) and carbon dioxide under geologic conditions. It is also a precursor to the production of silver nanoparticles.
It is explosive upon heating around 140 degrees Celsius, shock or friction.
Production.
Silver oxalate is produced by the reaction between silver nitrate and oxalic acid.


Bismuth oxychloride

Bismuth oxychloride is an inorganic compound of bismuth with the formula BiOCl. It is a lustrous white solid used since antiquity, notably in ancient Egypt. Light wave interference from its plate-like structure gives a pearly iridescent light reflectivity similar to nacre. It is also known as pearl white.
Structure.
The structure of bismuth oxychloride can be thought of as consisting of layers of Cl−, Bi3+ and O2− ions (in the image Bi = grey, O = red, Cl = green). These ions are ordered as Cl-Bi-O-Bi-Cl-Cl-Bi-O-Bi-Cl, i.e., with alternating anions (Cl−, O2−) and cations (Bi3+). The layered structure gives rise to the pearlescent properties of this material.
Focusing on the coordination environment of the individual ions, the bismuth centers adopt a distorted square antiprismatic coordination geometry. The Bi3+ ion is coordinated to four chloride, forming one of the square faces, each at a distance of 3.06 Å from Bi, and four oxygen atoms forming the other square face, each at a distance of 2.32 Å from Bi. The oxygen atoms are tetrahedrally coordinated by four bismuth atoms.
Synthesis and reactions.
BiOCl is formed during the reaction of bismuth chloride with water, i.e. the hydrolysis:
When heated above 600 °C, BiOCl converts to Bi24O31Cl10, called the "Arppe compound" which has a complex layer structure.
Use and occurrence.
It has been used in cosmetics since the days of ancient Egypt. It is part of the "pearly pigment found in eye shadow, hair sprays, powders, nail polishes, and other cosmetic products". Owing to the plate-like structure of the BiOCl, its suspensions exhibit optical properties like nacre.
In cosmetic its name is C.I. 77163.
BiOCl exists in nature as the rare mineral bismoclite, which is part of the matlockite mineral group.
An analogous compound, bismuth oxynitrate, is used as a white pigment.


Tungsten pentafluoride

Tungsten(V) fluoride is an inorganic compound with the formula WF5. It is a hygroscopic yellow solid. Like most pentafluorides, it adopts a tetrameric structure, consisting of [WF5]4 molecules. In this way, each W center achieves octahedral coordination.
Production.
Tungsten(V) fluoride is produced by the reaction of tungsten and tungsten hexafluoride:
At room temperature, it disproportionates to the tetra- and hexafluoride: