gas storage in porous 
 materials is a desirable technology that 
 has been significantly developed in recent years , owing to its potential 
 to address numerous persisting challenges in a number of industrial 
 applications related to energy , environment , and health care sectors . in the context of clean energy
, there is an amplified 
 willingness to reduce greenhouse gas emissions , caused by energy production 
 processes , as evidenced by the considerable ongoing research in academia 
 and industry alike aiming to develop practical solutions to mitigate 
 this problem .
correspondingly , appropriate studies have been conducted 
 in order to practically deploy relatively cleaner alternative fuels 
 such as methane ( ch4 ) , a primary component of natural gas 
 ( ng ) and biogas .
ch4 is of great interest as a fuel for 
 stationary and mobile applications due to ( i ) its high h to c ratio 
 in comparison to other fossil fuels , resulting in relatively lower 
 co and co2 emissions , and ( ii ) 
 its lower sulfur and nitrogen contents , leading to lessened sox and nox emissions . 

the aforementioned attributes position ch4 as a fuel appreciably 
 cleaner than gasoline and diesel .
nonetheless , 
 the main drawback of ch4 , in comparison to liquid fossil 
 fuels , is its low volumetric energy density .
therefore , the development 
 of suitable and sustainable on - board vehicle methane storage solutions , 
 close to room temperature , is vital to the successful deployment of 
 methane as a conventional fuel for transport applications .
highly porous materials represent an interesting 
 category of adsorbents 
 that display distinct structural advantages for ch4 storage . 

the appropriate combination of a high surface area associated with 
 a considerable pore volume with a suitable pore shape and functionality , 
 in a given porous material , is crucial to achieve the desired enhanced 
 ch4 storage uptake and a practical working capacity at 
 a set pressure and temperature .
it is 
 notable that the volumetric working capacity is an essential parameter 
 to assess the material s performance toward ch4 storage . 

the working capacity represents the usable amount of ch4 derived by subtracting the unused adsorbed ch4 , corresponding 
 to the uptake at the delivery pressure ( 5 bar ) , from the uptake at 
 the maximum adsorption pressure ( 35 bar or higher ) .
prominently , one of the pathways to enhance the methane 
 working capacity of a given porous material is to regulate its methane 
 uptake at relatively low pressures and subsequently reduce the unused 
 ch4 uptake up to the 5 bar threshold .
relatedly , 
 the storage of other gases such as nitric oxide ( no ) 
 and carbon dioxide ( co2 ) has been previously studied and 
 explored for various relevant applications .
in contrast , studies pertaining to high - pressure 
 oxygen ( o2 ) storage are still scarce .
the availability of high amounts of o2 is of 
 prime importance in the health care domain , particularly in the treatment 
 of respiratory insufficiencies and in hyperbaric oxygen changes for 
 the treatment of carbon monoxide poisoning .
correspondingly , a large 
 amount of oxygen is used to enrich air during catalyst regeneration 
 in the catalytic cracking units .
markedly , 
 there is a significant need to develop efficient pathways to store 
 o2 for various industrial needs . metal
 organic 
 frameworks ( mofs ) , a special class of solid - state 
 materials , have emerged as modular and functional porous materials 
 that can offer potential to address many enduring challenges pertaining 
 to energy and environmental sustainability .
principally , advances in mof chemistry have permitted the successful 
 implementation of reticular chemistry ; predesigned building blocks 
 were directed to assemble into a preset network topology .
namely , 
 the molecular building block ( mbb ) approach has been deployed to construct 
 targeted functional mofs , where desired structural and geometrical 
 attributes are incorporated into the mbbs prior to the assembly process . 
 in effect , isolating reaction conditions that consistently permit in situ formation of the requisite inorganic mbbs , in the 
 presence of a suitable organic linker , is essential for the successful 
 implementation of the mbb approach and the subsequent formation of 
 the targeted mof with the desired network topology .
advantageously , the mbb approach permits the rational 
 assembly 
 of targeted mofs and their subsequent structural fine tuning using 
 isoreticular chemistry .
the deliberate 
 alteration of a mof dimensionality and functionality without changing 
 its underlying topology , isoreticular chemistry , is regarded as a 
 powerful pathway for the development of new functional materials with 
 distinctive properties . evidently , the selection of an appropriate 
 mof platform , with desired 
 topological attributes for the logical practice of isoreticular chemistry , 
 offers the potential to readily access porous materials suitable to 
 address the ongoing gas storage challenges .
practically , several key requisites have been considered and targeted 
 in order to facilitate the attainment of a high - storage mof media : 
 ( i ) inorganic mbbs based on light and abundant elements , ( ii ) organic 
 mbbs amenable to size , shape , and functionality adjustments via expansion 
 and decoration , ( iii ) an elect mof platform that permits access to 
 isoreticular mofs with concomitant high surface area , large pore volume , 
 and fine - tuned pores in the micropore domain , and ( iv ) an mof platform 
 based on an underlying topology that prohibits interpenetration upon 
 mof expansion . in this context , considering the aforementioned 
 requisites , we 
 identified the mof platform based on the soc topology 
 ( square - octahedral ) as a promising 
 platform to access isoreticular mof materials for potential use in 
 gas storage and separation applications .
the soc - mof 
 platform offers interesting structural features where the pore system 
 comprised of cavities and channels can be fine tuned in the micropore 
 domain by the judiciously fine tuning the square building unit ( the 
 tetracarboxylate ligand ) .
it is notable 
 that the first reported soc - mof materials ( in- , ga- , 
 and fe - based soc - mof ) revealed an exceptionally high 
 gas storage density for h2 and ch4 despite their associated moderate surface area and pore volume in 
 comparison to the best storage mof materials .
congruently , we found it compelling to target soc - mofs 
 with relatively larger surface areas and pore volumes via isoreticular 
 chemistry , where the expansion strategy is employed to construct isoreticular soc - mofs based on selected / compatible and expanded organic 
 mbbs , and subsequently evaluate their performance for storage of valuable 
 commodities such as ch4 , h2 , co2 , 
 and o2 .
markedly , the construction of a highly microporous 
 mof with a soc topology requires the judicious selection 
 of an expanded 
 rectangular organic linker that facilitates the in situ formation of the targeted inorganic oxo - centered trinuclear m(iii ) 
 cluster [ m3(3-o)(o2c)6 ] ( m = in , al , fe , etc . ) .
specifically , targeting mofs based 
 on the trinuclear aluminum(iii ) cluster will permit the development 
 of a relatively low cost material with tailored properties for gas 
 storage applications .
it is important 
 to note that mofs based on the trinuclear al(iii ) cluster [ al3(3-o)(o2c)6 ] , a 6-connected mbb , are scarce , with only a few examples reported 
 in the literature due to challenges in isolating reaction conditions 
 that allow the in situ formation of the aforementioned 
 inorganic mbb . in this work ,
we 
 report the synthesis and the structure , on the 
 basis of single - crystal x - ray diffraction ( scxrd ) studies , of the 
 first aluminum mof having the soc topology and possessing 
 an exceptional porosity .
importantly , this is the first report disclosing 
 the assembly of the oxo - centered trinuclear aluminum(iii ) cluster 
 ( oxo - centered aluminum(iii ) trimer ) [ al3(3-o)(o2c)6 ] , with a quadrangular ligand 
 into a given mof , namely the highly microporous al - soc - mof-1 with more than 2 cm / g pore volume and 6000 m / g apparent langmuir surface area .
furthermore , the use of 
 similar reaction conditions , which afforded the synthesis of the parent 
 al - soc - mof-1 , in the presence of functionalized tetracarboxylate 
 linkers ( with naphthalene or anthracene replacing the phenyl core 
 in the parent ligand ) resulted in two new isoreticular structures : 
 namely the naphthalene species al - soc - mof-2 and the anthracene 
 species al - soc - mof-3 .
extensive gas adsorption studies 
 were carried out on these isoreticular soc - mofs with 
 different gases ( n2 , co2 , ch4 , o2 ) at low pressures ( cryogenic temperatures ) and at high pressures . 
 in particular , ch4 and o2 adsorption isotherms 
 were investigated experimentally at different temperatures and over 
 a wide range of pressures up to 85 and 120 bar , respectively .
it was 
 found that al - soc - mof-1 has one of the highest ever total 
 and working gravimetric ch4 uptakes at 35 bar and higher 
 pressures at any given temperature .
in contrast to all other best 
 mofs reported to date in the open literature for ch4 storage , 
 the parent al - soc - mof-1 sorption studies revealed an 
 enhancement in the volumetric ch4 storage working capacity 
 when the temperature was decreased .
particularly , at 258 k and 80 
 bar , the al - soc - mof-1 fulfilled the department of energy 
 ( doe ) target ( both gravimetric and volumetric ) and exhibited the highest 
 working volumetric capacity of 264 cm ( stp)/cm .
correspondingly , to the best of our knowledge , al - soc - mof-1 showed the highest gravimetric total capacity for co2 and o2 among microporous mofs .
furthermore , molecular 
 simulation studies supported and confirmed our experimental results 
 for ch4 storage and thus encouraged us to explore various 
 plausible theoretical isoreticular al - soc - mofs , based 
 on expanded ( or contracted ) and/or functionalized tetracarboxylate 
 organic building blocks , for ch4 storage .
this study permitted 
 us to ( i ) pinpoint various prospective al - soc - mofs with 
 outstanding ch4 storage capabilities similar to those of 
 the parent al - soc - mof-1 , confirming the superior volumetric 
 and gravimetric storage capabilities of the parent al - soc - mof-1 , and ( ii ) gain a better understanding of the structure 
property 
 relationship , deriving a better correlation between the soc - mof gas storage properties and the makeup of the soc - mof porous system ( pore shape and size , ligand dimensions and functionalities ) .
in our effort to isolate the first aluminum - based soc - mof , numerous attempts have been carried out to isolate 
 reaction 
 conditions that consistently allow the in situ formation 
 of the desired trinuclear aluminum(iii ) mbb [ al3(3-o)(o2c)6 ] .
accordingly , we 
 designed and synthesized the tetratopic ligand 3,3,5,5-tetrakis(4-carboxyphenyl)-p - terphenyl ( h4tcpt ) ( h4l1 ) that 
 can act as a rectangular mbb .
successfully , reactions between h4l1 and alcl36h2o in acidic solution containing a mixture of n , n-dimethylformamide ( dmf ) and 
 acetonitrile ( ch3cn ) afforded colorless homogeneous crystals 
 with a cube - shaped morphology , characterized and formulated by scxrd 
 as [ al3o(tcpt)1.5(h2o)3]|cl| ( 1 ) .
the crystal structure of 1 reveals a 3-periodic 
 framework built up from 3-oxo - centered trinuclear 
 al(iii ) inorganic mbbs [ al3(3-o)(h2o)3(o2c)6 ] .
each 
 aluminum cation ( al ) displays an octahedral coordination 
 environment and coordinates to six oxygen atoms : namely , four bis - monodentate 
 deprotonated carboxylate oxygen atoms from four independent tcpt ligands and one 3-oxo anion , and 
 a terminal aqua ligand to complete the coordination sphere .
the trinuclear 
 al(iii ) mbbs are bridged by six independent tcpt ligands , resulting in the formation of a 3-periodic cationic framework , 
 al - soc - mof-1 ( figure 1 ) .
the charge balance is provided by the presence of 
 chloride ions , which was confirmed by an x - ray photoelectron spectroscopy 
 ( xps ) experiment ( figure s11 in the supporting 
 information ) .
crystallographic analysis affirms that the chloride 
 ions are disordered over six positions around the trinuclear al(iii ) 
 cluster with equal probability .
this analysis was also supported by 
 a al solid - state nmr spectroscopy experiment ( figure s12 in the supporting information ) .
crystal structure 
 of 1 showing the assembly of the 
 trinuclear aluminum(iii ) mbb [ al3(3-o)(h2o)3(o2c)6 ] with the 
 organic ligand h4tcpt ( h4l1 ) ( middle ) 
 and topological analysis of 1 , where the 6-connected 
 trinuclear al(iii ) mbb can be viewed as a trigonal - prismatic sbu , 
 while the organic ligand can be rationalized as a 4-connected building 
 unit to give ( 4,6)-c soc - net ( left ) or can be viewed 
 as 3-c sbus resulting in a ( 3,6)-c derived net edq ( right ) .
topological analysis reveals that 1 has the anticipated 
 edge transitive ( 4,6)-connected net with the soc underlying 
 topology .
the trinuclear al(iii ) mbb [ al3(3-o)(o2c)6 ] can be regarded as a trigonal - prismatic 
 secondary building unit ( sbu ) with the six points of extension corresponding 
 to the carbon of the carboxylate moieties matching the vertex figure 
 of the 6-c node in the soc net .
the 6-c inorganic mbbs 
 are joined by the rectangular organic ligand , 4-c node , into a primitive 
 cubic system arrangement ( figure 1 ) . alternatively from 
 a topological perspective
, the 4-c rectangular ligand can be regarded 
 as comprised of two interconnected 3-c triangular sbus that are further 
 linked through the 6-c trigonal - prismatic sbus to afford a mof related 
 to a ( 3,6)-c derived net edq , with transitivity 2 2 ( figure 1 and figures s25 and s26 in the supporting information ) . in this paper , the reported al - mofs
will be referred to as al - soc - mofs . in order to isolate other isoreticular analogues 
 of al - soc - mof-1 , the phenyl ring located at the core 
 of the h4tcpt 
 ligand
was substituted by 1,4-naphthalenyl and 9,10-anthracenyl cores 
 to give the naphthalene- and anthracene - functionalized ligands 3,3,5,5-tetrakis(4-carboxyphenyl)-1,4-diphenylnaphthalene 
 ( h4tcdpn ) ( h4l2 ) and 3,3,5,5-tetrakis(4-carboxyphenyl)-9,10-diphenylanthracene 
 ( h4tcdpa ) ( h4l3 ) , respectively ( figure 2a ) .
as anticipated , under 
 reaction conditions similar to those used to isolate the al - soc - mof-1 , cube - shaped crystals were obtained and characterized 
 using scxrd and powder x - ray diffraction ( pxrd ) studies ( figure 2b ) , revealing the 
 construction of two isoreticular al - soc - mof compounds , 
 naphthalene al - soc - mof-2 ( 2 ) and anthracene 
 al - soc - mof-3 ( 3 ) with the formula [ al3o(ligand)1.5(h2o)3]|cl| .
( a ) representation of the organic mbbs used to construct 
 isoreticular 
 al - soc - mofs .
( c ) nitrogen isotherms at 77 k for the isoreticular 
 al - soc - mofs .
the phase purity of each al - soc - mof compound 
 ( 13 ) was confirmed by whole profile 
 pattern 
 matching using the le bail method ( figures s13s15 in the supporting information ) .
the al - soc - mof-1 structure encloses cubic - shaped cages 
 14.3  in diameter delimited by six tcpt ligands , 
 which occupy the faces of the cage , and eight inorganic trinuclear 
 al(iii ) clusters located on the vertices of the cuboidal cage .
the 
 cage is accessible through apertures of approximately 5.6  8.4 
  , taking van der waals ( vdw ) radii into consideration .
the structure 
 also encloses two well - defined 1d infinite channels with estimated 
 dimensions of 14  ( vdw ) , which is approximately at the border 
 of microporous materials ( figures s23 and s24 in the supporting information ) .
the corresponding solvent - accessible 
 free volumes for 13 were estimated 
 to be 80.5% , 79% , and 75% , 
 respectively , by summing voxels more than 1.2  away from the 
 framework using platon software . in light of
the extraordinarily pure microporous architecture exhibited 
 by 13 , optimization of the conventional 
 activation conditions ( drying under vacuum and heating ) showed that 
 the guest solvent in the pores could be easily removed using a traditional 
 approach ( vacuum and heating ) without altering their microporosity . 

nitrogen ( n2 ) adsorption measurements at 77 k were carried 
 out on the acetonitrile - exchanged samples , showing a fully reversible 
 type i isotherm representative of porous materials with permanent 
 microporosity ( figure 2c ) .
g for 2 , and 5212 and 4849 cm / g for 3 ( table 1 ) .
it is notable that the resultant high microporosity ( surface 
 area and pore volume ) is exceptional and has not been observed , prior 
 to this work , using a traditional activation method that often causes 
 pore collapse in the case of highly porous mofs .
such a unique feature is of prime importance for the implementation 
 and deployment of 13 as gas storage 
 media for onboard or stationary gas storage applications . abet and alang are the experimental 
 bet and 
 langmuir specific surface areas .
pvtheo and pvexp are the calculated pore volume from crystal structures and the experimentally 
 measured pore volume , respectively .
the successful use of the conventional activation 
 method was confirmed 
 by the excellent agreement between the experimental and the optimal 
 theoretical pore volumes ( pvexp = 2.3 , 2.1 , and 1.8 cm / g and pvtheo = 2.3 , 2.2 , and 1.9 cm / g for 13 , respectively ) .
furthermore , 
 al - soc - mof structures preserved their optimal porosity 
 after heating up to 340 c under vacuum ( figures s27b , s34b , and s36b in the supporting information ) , 
 another essential feature that is rarely observed for highly porous 
 mofs .
the high thermal stability was also confirmed using variable - temperature 
 pxrd studies and thermal gravimetric analysis ( figures s17s22 in the supporting information ) .
interestingly , the extremely 
 open structure , exclusively concerted in the microporous range , combined 
 with the distinctive structural features ( presence of cages and channels ) 
 place al - soc - mofs as ideal adsorbent candidates for gas 
 storage studies . accordingly , ch4 adsorption on 13 was extensively studied experimentally at 
 variable temperatures and up to 80 bar as well as at low pressure 
 and 112 k ( boiling point of ch4 ) .
the methane adsorption 
 isotherms at 112 k for 13 revealed 
 remarkable ch4 uptakes near saturation pressures e.g. , 
 1336 , 1205 , and 1055 cm ( stp)/g at p / p0 = 0.95 , respectively ( figures s28a , s35a , and s37a in the supporting information ) . 

importantly , high - pressure ch4 adsorption isotherms at 
 variable temperatures , depicted in figure 3 , showed that 1 has one of the 
 highest ch4 gravimetric uptakes ever reported ( ca .
361 
 cm ( stp)/g ) for any microporous mof materials under the 
 disclosed doe operational storage conditions ( 298 k and 35 bar ) .
mesoporous 
 mof-210 and dut-49 displayed uptakes of around 210 and 364 cm(stp)/g 
 under the same conditions .
interestingly , the doe ch4 gravimetric 
 uptake target of 700 cm ( stp)/g ( 0.5 g / g ) was addressed 
 and reached for relatively high pressures at temperatures below 288 
 k : e.g. 50 bar at 258 k and 85 bar at 288 k ( figure 3 ) .
single - component gas adsorption isotherms for 
 ch4 at 
 different temperatures for al - soc - mof-1 , showing total 
 ch4 gravimetric uptakes surpassing the doe target at particular 
 pressures and temperatures .
additionally , analysis of the volumetric ch4 adsorption 
 isotherms , using the al - soc - mof-1 crystal density , revealed 
 an enhancement in the volumetric ch4 storage working capacity 
 when the temperature was decreased ( figure 4 ) .
specifically , the volumetric ch4 storage working capacity for 1 increased from 201 cm ( stp)/cm to 264 cm ( stp)/cm when the temperature was decreased from 298 to 258 k at working 
 pressures between 80 bar ( adsorption ) and 5 bar ( desorption ) .
this 
 attribute , unique to al - soc - mof-1 , is unprecedented , 
 as all available ch4 storage data for mofs have shown a 
 conventional decrease in the volumetric ch4 storage working 
 capacity with a decrease in temperature , as illustrated in figure 4 and table s3 in the supporting information for utsa-76 , hkust-1 , ni - mof-74 , nu-111 , and pcn-14 .
it is notable that mof-519 was not 
 included in this comparative assessment , as the associated data at 
 low temperatures were not available for this highly ch4 adsorbing mof .
comparison of the ch4 volumetric working capacities 
 ( 580 and 565 bar ) at different temperatures ( 258 , 
 273 , and 298 k ) for al - soc - mof-1 with the best microporous 
 mof materials reported to date .
a comprehensive comparison of absolute ch4 uptakes 
 and 
 working capacities for al - soc - mof-1 ( 1 ) 
 with the various best mof materials reported so far under different 
 temperature and pressure conditions is presented in figure 5 and figure s38 in the supporting information .
interestingly , although 
 the total volumetric ch4 uptake for 1 is relatively 
 lower than those of some of the highly adsorbing mofs , 1 displayed mutually high volumetric and gravimetric working capacities 
 at different working temperatures and pressures .
this notable and 
 rare compromise between the gravimetric and the volumetric capacities 
 for 1 is a result of the reduced unused ch4 uptake below 5 bar and the linear trend of the ch4 isotherms 
 at relatively high pressures , a desirable attribute for an appropriate 
 gas storage medium .
in contrast to the best mofs reported so far for 
 ch4 storage , 1 exhibits a relatively low ch4 heat of adsorption ( 11 kj / mol at low loading ) in the relatively 
 low ch4 loading region , only slightly higher than the ch4 latent heat of evaporation ( figure s30 in the supporting information ) .
markedly , the comparatively favorable 
 methane adsorption at relatively high pressures can be attributed 
 to enhanced ch4ch4 interactions regulated 
 by the appropriate pore size of al - soc - mof-1 .
therefore , 
 the combination of both aforementioned effects , governing the ch4 adsorption at low and high pressures , in a single material 
 afforded the exceptional ch4 working capacities observed 
 for the al - soc - mof-1 , especially at relatively low temperatures . 

it is notable that 1 exhibits the second highest ch4 volumetric working capacity at 298 k and 580 bar 
 working pressure range : namely , 201 cm ( stp)/cm vs 230 cm ( stp)/cm for the recently reported 
 mof-519 .
noticeably , the two synthesized isoreticular al - soc - mofs ( 2 and 3 ) also exhibited high gravimetric 
 and volumetric total and working ch4 uptakes that were 
 only slightly lower than the uptake values derived for 1 .
the experimental results for 2 and 3 are 
 summarized in figure s41 and table s4 in 
 the supporting information .
total ( a  d ) at 65 and 80 bar and 565 
 and 580 
 bar working ( e  h ) ch4 gravimetric and volumetric 
 uptakes for al - soc - mof-1 ( 1 ) in comparison 
 to the best mof materials reported to date at 298 , 270 , and 240 k. 
 the data for al - soc - mof-1 ( 1 ) were collected 
 at 298 , 273 , and 258 k. with 
 the aim of gaining a better understanding of the structure 
property 
 relationship governing the resultant high methane storage capacities 
 in the al - soc - mofs , we assessed theoretically the plausible 
 ch4 storage capacity of various plausible theoretical isoreticular 
 al - soc - mofs based on expanded ( or contracted ) and/or 
 functionalized tetracarboxylate organic building blocks . in 
 order to derive a better correlation between the soc - mof 
 gas storage properties and the makeup of the soc - mof 
 porous system ( pore shape and size , ligand dimensions and functionalities ) , 

a comprehensive molecular simulation study was carried out on various 
 hypothetical / isoreticular al - soc - mofs constructed using 
 hypothetical organic building blocks .
first , we envisioned validating 
 our molecular simulation methodology on the parent 1 ( al - soc - mof-1 ) and corroborating the mechanism of ch4 adsorption at 5 bar and at higher pressures , resulting in the outstanding 
 ch4 working capacity .
second , we simulated and evaluated 
 the absolute and working ch4 uptakes for various hypothetical 
 isoreticular soc - mofs , constructed using different optimized 
 ( i ) elongated , ( ii ) functionalized , and ( iii ) contracted organic mbbs . 
 in effect , the simulated isoreticular al - soc - mofs were 
 assembled using both experimentally synthesized and hypothetically 
 designed linkers obtained by modifying the arms and/or the core of 
 the al - soc - mof-1 ligand as shown in figure 6 and figure s47 and scheme s2 in the supporting information .
figure 6 depicts the naming scheme 
 employed to label the hypothetical al - soc - mof linkers . 

for example , the original linker is shown in figure 6 ( left ) , where p - p denotes phenyl  phenyl : 
 both the arm and the core have one phenyl group .
phenyl for the arm and acetylene  phenyl  acetylene 
 for the core , as shown in figure 6 ( right ) .
a total of 18 theoretical analogues were 
 hypothetically assembled , and their associated ch4 adsorption 
 isotherms were simulated . for clarity
the new simulated al - soc - mof structures will be named and referred to using the associated 
 linker name .
scheme illustrating the adapted naming for the employed 
 hypothetical 
 organic ligands and associated hypothetical al - soc - mofs .
initially , grand canonical monte 
 carlo ( gcmc ) simulations of methane 
 adsorption were performed for the parent compound 1 in 
 order to compare first the resulting simulated results with available 
 experimental adsorption data , and subsequently validate the simulation 
 approach adopted in this study ( figure 7a and figure s44 in the 
 supporting information ) .
more details about the employed simulation 
 method are described in the supporting information . as shown
, the theoretical ch4 adsorption isotherm for p - p is in a good agreement with the experimental data ( 1 ) .
the corresponding screenshots of methane adsorption at 
 different relevant pressures , i.e. 5 bar ( limiting desorption pressure ) 
 and 35 , 65 , and 80 bar ( storage pressures ) , are shown in figure 7b .
the relatively 
 very low simulated unused methane uptake at 5 bar ( both gravimetric 
 and volumetric ) for p - p equivalent to 1 , 
 at 5 bar , was confirmed by performing adsorption isotherms at different 
 temperatures : namely , at 298 , 295 , 273 , and 258 k ( figure s45 in the supporting information ) .
this is reflected 
 in the observed nonpreferential positions of ch4 molecules 
 in the framework of p - p ( figure 7b ) : i.e. , no specific preferential adsorption 
 sites at 5 bar .
( a ) methane sorption in al - soc - mof-1 at 298 
 k : simulation 
 ( red filled circles ) vs experiment ( black filled squares ) .
( b ) screenshots 
 of methane adsorption in p - p ( equivalent to al - soc - mof-1 ) at 298 k at different pressures : 5 , 35 , 65 , and 
 80 bar .
the purple spheres surrounding the framework represent the 
 methane molecules . delightfully , the simulated 
 ch4 adsorption isotherms 
 on the optimized structure , on the basis of a molecular mechanics 
 simulation approach ( details in the supporting information ) , of the parent 1 ( p - p ) are in good agreement with the corresponding ch4 adsorption 
 isotherms simulated on the experimental structure ( figure s46 in the supporting information ) .
accordingly , the 
 same molecular mechanics optimization procedure was employed to construct 
 18 hypothetical isoreticular al - soc - mofs and subsequently 
 simulate their associated total and working ch4 uptakes 
 using the gcmc approach .
the simulated absolute volumetric and 
 gravimetric ch4 adsorption isotherms for p - p ( 1 ) and the 
 other isoreticular al - soc - mofs were simulated at various 
 temperatures and up to 80 bar total pressure ( figures s76s84 in the supporting information ) .
interestingly , these results showed that the use of ( i ) elongated , 
 ( ii ) functionalized , and ( iii ) contracted linkers resulted in three 
 distinguished al - soc - mof groups in terms of gravimetric  volumetric 
 uptake tradeoff .
in fact , the use of ( i ) elongated arms and/or cores , 
 such as pp - pp , led to an increase in the gravimetric 
 uptake at the expense of the volumetric uptake under any pressure 
 and temperature conditions evaluated in this study .
( ii ) functionalizing 
 the phenyl core of the linker led generally to lower gravimetric uptake 
 but still with good gravimetric  volumetric uptake tradeoff 
 under any pressure and temperature conditions explored here . in a 
 particular case , strategies for functionalization of the phenyl cores 
 with different functional groups , such as cf3 and br , led 
 to relatively good working volumetric uptakes ( due to the relatively 
 higher framework density ) , albeit with much lower working gravimetric 
 uptakes .
interestingly , ( iii ) contraction of the arms and/or the core , 
 for instance the a - p structure , offer potential for a 
 collective improvement ( ideal compromise ) of the gravimetric and volumetric 
 uptakes in comparison to 1 at any temperature , particularly 
 at intermediate pressures of 35 bar ( figure 8) .
principally , in terms of ch4 working ( 535 bar ) volumetric and gravimetric capacity tradeoff , 
 contraction of the arms showed a notable improvement in the absolute 
 ch4 uptake at 298 k. this unique compromise can be attributed 
 to the enhanced ch4 adsorption uptake at relatively high 
 pressures below 35 bar , due to the reduced channel dimensions in the a - p structure in comparison to the parent al - soc - mof-1 ( 9.3   10.0  vs 14.0   14.2 
  ) .
it is important to note that the al - soc - mof-1 
 ( p - p ) still exhibits both enhanced volumetric and gravimetric 
 tradeoff for 565 and 580 bar working pressures at 
 any temperature ( figure 8) .
total ( a ) at 35 bar and ( b ) 535 bar working ch4 gravimetric and volumetric uptakes for p - p and a - p simulated structures in comparison to the best mof materials 
 reported to date at 298 k. theoretical total ( left , c and e ) and working 
 ( right , d and f ) gravimetric vs volumetric capacities for selected 
 hypothetical isoreticular al - soc - mofs under a wide range 
 of pressures ( 35 , 65 , and 80 bar ) at different temperatures ( 298 and 
 258 k ) in comparison to al - soc - mof ( 1 ) . 

the purple area represents the desired range of the best compromise 
 between gravimetric and volumetric total and working uptakes .
a summary of the theoretical results 
 in terms of ch4 absolute and working capacities , volumetric 
 and gravimetric , at 
 298 , 273 , and 258 k under a wide range of pressures are presented 
 in figures s48s66 in the supporting 
 information .
the 
 exceptional methane storage capabilities of al - soc - mof-1 
 have inspired us to extend this study to other important commodities , 
 namely o2 and co2 .
accordingly , we recorded 
 various o2 and co2 adsorption isotherms for 
 al - soc - mof-1 .
notably , the amounts of o2 and 
 co2 adsorbed in al - soc - mof-1 near saturation 
 pressures ( 0.95 p / p0 ) , 
 derived from adsorption isotherms at 90.2 and 195.15 k for o2 and co2 , respectively , were found to be remarkably high 
 ( 1757 and 1236 cm ( stp)/g , respectively ) ( figure s29 in the supporting information ) .
markedly , 
 the combination of experimentally accessible low pressure ( at 90.2 
 k ) and high - pressure o2 adsorption data up to 115 bar ( at 
 298 k ) ( combined with the toth model ) revealed that al - soc - mof-1 exhibits a record of 29 mmol / g absolute gravimetric o2 uptake at 140 bar , which is much higher than those of hkust-1 
 ( 13.2 mmol / g ) and nu-125 ( 17.4 mmol / g ) , reference materials for this application ( figure 9 ) .
additionally , 
 al - soc - mof-1 displayed a record deliverable capacity 
 between 5 and 140 bar of 27.5 mmol / g , vs 11.8 and 15.4 mmol / g for 
 hkust-1 and nu-125 , respectively ( figure 9a ) .
consequently , by neglecting the effect 
 of packing density and the void space occupied by the material , a 
 1 l cylinder filled with al - soc - mof-1 will potentially 
 enhance the volumetric o2 storage capacity ( 172 cm / cm ) by 70% at 100 bar , in comparison to a conventional 
 empty cylinder ( figure 9b ) .
it is notable that , if we assume a prospective 
 25% loss associated with packing density , the al - soc - mof-1 
 volumetric o2 storage capacity still offers a 25% enhancement 
 over an empty cylinder .
analysis of the o2 adsorption recorded 
 at variable temperatures indicated that 1 exhibits a 
 relatively low o2 heat of adsorption ( 10 kj / mol at low 
 loading ) over the whole o2 loading range , slightly higher 
 than the o2 latent heat of evaporation ( figure s33 in the supporting information ) .
( a ) single - component 
 gravimetric gas adsorption isotherm for o2 at 298 k showing 
 that 1 exhibits the highest 
 deliverable uptake reported so far .
( b ) volumetric o2 adsorption 
 isotherm compared to the storage capacity in a pressurized container .
additionally , the co2 adsorption studies revealed 
 that 
 al - soc - mof-1 exhibits an exceptional absolute gravimetric 
 co2 uptake at 40 bar of 2 g / g ( 1020 cm ( stp)/g ) 
 vs 1.5 g / g for mof-177 , setting a new record among microporous mofs 
 ( figure s39 in the supporting information ) . 

consequently , al - soc - mof-1 displays the uppermost working 
 capacity between 1 and 40 bar of 1.90 g / g ( 967 cm ( stp)/g ) 
 vs 1.46 g / g ( 742 cm ( stp)/g ) for mof-177 .
an analysis of variable - temperature co2 adsorption data showed that al - soc - mof-1 exhibits 
 a relatively low co2 heat of adsorption ( 17 kj / mol at low 
 loading ) over the whole co2 loading range ( figure s31b in the supporting information ) .
it 
 is important to note that the mesoporous mof-210 exhibits the highest absolute gravimetric co2 uptake at 50 bar ( 2.8 g / g ) .
finally , it is worth noting that 
 al - soc - mof-1 also 
 exhibits an excellent h2 storage capacity at 77 k ( ca . 

11 wt % ) ( figure s40 in the supporting 
 information ) at high pressure ( 30 bar ) in comparison to other highly 
 porous materials . similarly , o2 and co2 adsorption studies 
 were performed for the two isoreticular al - soc - mofs ( 2 and 3 ) , which revealed that the naphthalene 
 and anthracene analogues exhibit only slightly lower o2 and co2 adsorption uptakes under the same conditions 
 in comparison to 1 ( figures s42 and s43 and table s4 in the supporting information ) .
in summary , we successfully employed the molecular building block 
 approach to synthesize the first aluminum soc - mof isoreticular 
 materials . specifically , reaction conditions that consistently permit 
 the in situ generation of the [ al3(3-o)(h2o)3(o2c)6 ] mbb were isolated and used for the construction of a highly 
 porous ( 4,6)-connected aluminum based soc - mof , al - soc - mof-1 , with more than 6000 m / g langmuir specific 
 surface area .
importantly , tedious activation using dry supercritical 
 co2 is not required in order to activate the al - soc - mof-1 and its naphthalene and anthracene analogues .
in particular , 
 the conventional activation technique , i.e. a simple combination of 
 heating and vacuum ( or n2 flush ) , is sufficient for full 
 activation prior to gas loading  unloading cycles .
extensive 
 gas adsorption studies were carried out on the al - soc - mof platform with different gases ( n2 , co2 , ch4 , o2 , etc . ) .
methane adsorption 
 isotherms were completed at different temperatures and over a wide 
 range of pressures , up to 85 bar .
interestingly , it was found that 
 al - soc - mof-1 exhibits one of the highest total and working 
 gravimetric ch4 uptakes at 35 bar .
in contrast to the other 
 reported best mofs for ch4 storage , al - soc - mof-1 showed enhanced ch4 storage working capacity as 
 the temperature was decreased . particularly , at 258 k and 80 bar , 
 al - soc - mof-1 fulfils the doe target and exhibits the 
 highest working volumetric capacity of 264 cm ( stp)/cm . to the best of our knowledge , this is the first time that 
 a porous material has fulfilled both the challenging gravimetric and 
 volumetric targets for the ch4 working capacity .
the collective 
 experimental and gcmc simulation studies indicated that the parent 
 al - soc - mof-1 , in contrast to various hypothetical isoreticular 
 al - soc - mofs based on contracted , elongated , and functionalized 
 ligands , exhibits the best compromise between the volumetric and gravimetric 
 total and working uptakes over a wide range of pressure and temperature 
 conditions .
details on the synthesis of the 
 organic ligands used in this study , 3,3,5,5-tetrakis(4-carboxyphenyl)-p - terphenyl ( h4tcpt ) , 3,3,5,5-tetrakis(4-carboxyphenyl)-1,4-diphenylnaphthalene 
 ( h4tcdpn ) , and 3,3,5,5-tetrakis(4-carboxyphenyl)-9,10-diphenylanthracene 
 ( h4tcdpa ) , are provided in 
 the supporting information .
single - crystal 
 diffraction data were collected at beamline i19 , diamond light source , 
 didcot , u.k . , using the wavelength  1.0402  at 250 k. 
 fourier - transform infrared ( ft - ir ) spectra ( 4000600 cm ) were collected in the solid state on a nicolet 700 
 ft - ir spectrometer .
the peak intensities are described in each of 
 the spectra as very strong ( vs ) , strong ( s ) , medium ( m ) , weak ( w ) , 
 broad ( br ) , and shoulder ( sh ) .
powder x - ray diffraction ( pxrd ) measurements 
 were performed on a panalytical mpd xpert pro x - ray diffractometer 
 at 45 kv and 40 ma for cu k (  1.5418  ) equipped 
 with a variable - temperature stage , with a scan speed of 20/min . 

the sample was held at the designated temperature for at least 10 
 min between each scan . high - resolution dynamic thermal gravimetric 
 analysis ( tga ) was performed under a continuous n2 flow 
 and recorded on a ta instruments high - resolution tgaq500 thermogravimetric 
 analyzer .
low - pressure gas sorption measurements were performed on 
 a fully automated autosorb-1c gas sorption analyzer ( quantachrome 
 instruments ) .
high - pressure gas sorption studies were performed with 
 a magnetic suspension balance marketed by rubotherm ( bochum , germany ) .
a solution of alcl36h2o ( 29 
 mg , 0.015 mmol ) and h4l1 ( 7.1 mg , 0.01 mmol ) in n , n - dimethylformamide 
 ( dmf ) ( 1 ml ) , acetonitrile ( ch3cn ) ( 1 ml ) , and nitric acid 
 ( 3.5 m , 0.5 ml ) was prepared in a 20 ml scintillation vial and subsequently 
 placed into a preheated oven at 130 c for 12 h to give pure 
 small colorless cube - shaped crystals .
suitable single crystals were 
 obtained using the same synthetic procedure , but with an increase 
 in the amount of hno3 to l ml .
crystals of al - soc - mof-1 were harvested , washed with ch3cn , and air - dried . 

ft - ir ( 4000650 cm ) : 3349 ( br ) , 1605 ( s ) , 
 1592 ( s ) , 1423 ( s ) , 1387 ( vs ) , 1312 ( w ) , 1243 ( w ) , 1100 ( w ) , 1018 
 ( w ) , 854 ( w ) , 830 ( w ) , 783 ( s ) , 771 ( s ) , 701 ( s ) . a 
 solution of alcl36h2o ( 29 
 mg , 0.015 mmol ) and h4l2 ( 7.6 mg , 0.01 mmol ) in n , n - dimethylformamide 
 ( dmf ) ( 1 ml ) , acetonitrile ( ch3cn ) ( 1 ml ) , and nitric acid 
 ( 3.5 m , 0.5 ml ) was prepared in a 20 ml scintillation vial and subsequently 
 placed into a preheated oven at 130 c for 12 h to give pure 
 small colorless cube - shaped crystals .
suitable single crystals were 
 obtained using the same synthetic procedure , but with an increas in 
 the amount of hno3 to l ml .
crystals of al - soc - mof-2 were harvested , washed with ch3cn , and air - dried . 

ft - ir ( 4000650 cm ) : 3349 ( br ) , 1606 ( s ) , 
 1545 ( m ) , 1422 ( s ) , 1384 ( s ) , 1241 ( w ) , 1100 ( w ) , 1015 ( w ) , 851 ( w ) , 
 851 ( w ) , 771 ( s ) , 705 ( m ) .
a solution of alcl36h2o ( 29 
 mg , 0.015 mmol ) and h4l3 ( 8.1 mg , 0.01 mmol ) in n , n - dimethylformamide 
 ( dmf ) ( 1 ml ) , acetonitrile ( ch3cn ) ( 1 ml ) , and nitric acid 
 ( 3.5 m , 0.3 ml ) was prepared in a 20 ml scintillation vial and subsequently 
 placed into a preheated oven at 130 c for 12 h to give a pure 
 microcrystalline yellow powder .
suitable single crystals were obtained 
 using the same synthetic procedure , but with an increase in the amount 
 of hno3 to 1 ml crystals of al - soc - mof-3 were 
 harvested , washed with ch3cn , and air - dried .
ft - ir ( 4000650 
 cm ) : 3349 ( br ) , 1606 ( s ) , 1547 ( s ) , 1442 ( s ) , 
 1387 ( s ) , 1312 ( w ) , 1241 ( w ) , 1181 ( w ) , 1016 ( w ) , 852 ( m ) , 771 ( s ) , 
 706 ( s ) .
 the molecular building block approach 
 was employed effectively 
 to construct a series of novel isoreticular , highly porous and stable , 
 aluminum - based metal  
 organic frameworks with soc topology . from this platform , 
 three compounds were experimentally 
 isolated and fully characterized : namely , the parent al - soc - mof-1 and its naphthalene and anthracene analogues . 
 al - soc - mof-1 exhibits outstanding gravimetric methane uptake ( total and 
 working capacity ) . 
 it is shown experimentally , for the first time , 
 that the al - soc - mof platform can address the challenging 
 department of energy dual target of 0.5 g / g ( gravimetric ) and 264 
 cm3 ( stp)/cm3 ( volumetric ) methane storage . 
 
 furthermore , al - soc - mof exhibited the highest total gravimetric 
 and volumetric uptake for carbon dioxide and the utmost total and 
 deliverable uptake for oxygen at relatively high pressures among all 
 microporous mofs . in order to correlate the mof pore structure and 
 functionality to the gas storage properties , to better understand 
 the structure  property relationship 
 , we performed a molecular 
 simulation study and evaluated the methane storage performance of 
 the al - soc - mof platform using diverse organic linkers . 
 
 it was found that shortening the parent al - soc - mof-1 
 linker resulted in a noticeable enhancement in the working volumetric 
 capacity at specific temperatures and pressures with amply conserved 
 gravimetric uptake / working capacity . 
 in contrast , further expansion 
 of the organic linker ( branches and/or core ) led to isostructural 
 al - soc - mofs with enhanced gravimetric uptake but noticeably 
 lower volumetric capacity . 
 the collective experimental and simulation 
 studies indicated that the parent al - soc - mof-1 exhibits 
 the best compromise between the volumetric and gravimetric total and 
 working uptakes under a wide range of pressure and temperature conditions . 
Introduction
Results
and Discussion
Conclusions
Experimental Section