Cinnabar akin to that of HgO: each Hg center has two short Hg−S bonds (each 2.36 Å), and four longer contacts (with 3.10, 3.10, 3.30, and 3.30 Å separations). In addition, HgS is found in a black, non-cinnabar polymorph (metacinnabar) that has the zincblende structure. Cinnabar generally occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs. Cinnabar is deposited by epithermal ascending aqueous solutions (those near surface and not too hot) far removed from their igneous source. It is associated with native mercury, stibnite, realgar, pyrite, marcasite, opal, quartz, chalcedony, dolomite, calcite and barite. Cinnabar is
Metal ammine complex is ammonia (pK ~ 33). For highly cationic complexes such as [Pt(NH)], the conjugate base can be obtained. The deprotonation of cobalt(III) ammine-halide complexes, e.g. [CoCl(NH)] labilises the Co-Cl bond, according to the Sn1CB mechanism. Metal ammine complexes find many uses. Cisplatin (PtCl(NH)) is a coordination compound containing two chloro and two ammine ligands. This is a drug used in treating cancer. Many other amine complexes of the platinum group metals have been evaluated for this application. In the separation of the individual platinum metals from their ore, several schemes rely on the precipitation of [RhCl(NH)]Cl. In some separation schemes,