Rhenium heptafluoride, structure

The number of species isoeiectronic with XeF, is quite limited. The anions SbBr, TeCl , and TeBr are octahedral. Both IF and XeF are nonoctahedral." Iodine heptafluoride and rhenium heptafluoride may be considered isoeiectronic with these species if they are all considered to have 14 valence shell electrons of approximately equal steric requirements. Both have a pentagonal bipyramidal structure (see Fig. 6.12). Most interestingly, the XeF anion, formed by the Lewis acid XeF ... 

Vogt T, Fitch AN, Cockcroft JK (1994) Crystal and molecular structures of rhenium heptafluoride. Science 263 1265-1267... 

Only two transition metal heptafluorides are known. Rhenium hep-tafluoride is stable, but osmium heptafluoride is so unstable that no structural results for the solid compound have been reported (4). The rhenium compound is cubic (92) at room temperature, with unit-cell dimension a = 6.26(2) A, which is the same as that for rhenium hexafluoride (Table V). This cubic form is stable to -90°C, when a transition occurs to a form of lower symmetry, for which unit-cell dimensions are unknown (92). 

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