Iridium pentafluoride, structure

Table 2 gives some of the physical properties of the known pentafluorides. Iridium pentafluoride is isomorphous and nearly isodimensional with ruthenium pentafluoride and presumably has the nonlinear fluorine-bridged tetrameric molecular structure, reported by Holloway, Peacock, and Small for that fluoride. In this arrangement the... 

Although a number of complex fluorides of quinquevalent iridium, (e.g. KIrF,) are known, previous attempts to establish the simple fluoride have failed. The absence of a pentafluoride of iridium has become increasingly anomalous as the pentafluorides of the neighbouring elements, rhenium, osmium, and platinum have been prepared. Previous work - indicated that reactions which might have yielded the pentafluoride gave the tetrafluoride instead. The physical properties of this tetrafluoride. (m.p. 106—107 b.p. > 300 ), however, resembled those of a pentafluoride or oxide tetrafluoride. This indicated that iridium tetrafluoride differed structurally from its neighbouring tetrafluorides. 

Rhodium pentafluoride is isomorphous with its ruthenium, osmium, and iridium analogues, the crystal data being a, 12-28 b, 9-86 c, 6-48 A ]3, 99-2° Uobs-, 654-2 A Z = 8. Presumably the structural unit of this compound is a fluorine-bridged tetramer, as in ruthenium pentafluoride. It is noteworthy that the unit-cell volume is smaller than in the ruthenium analogue, possibly as a... 

In 1958, the fluoride long known[l] as OsFg was shown by Weinstock and Malm [2] to be OsFg and, in 1965, the fluoride of iridium, reported [3,4] on two occasions to be a tetraflu.oride was shown [5] by Bartlett and Rao to be a pentafiuoride. New hexafluorides [4,6-8] and pentafiuorides[9-ll] (in addition to RuFj which had long been known) have now established hexafluorides and pentafluorides for all of the platinum metals other than palladium. Moreover, the trifluorides, RuFj, RhFr, PdFi and IrFr have been established by X-ray crystal structure analysis [12] although that of palladium has been shown [13] to be the mixed oxidation state compound Pd(II) Pd(IV)F6. So far only one di-fluoride of the platinum metals, PdF2, has been reported[14-16]. 

Rhodium(VI) and iridium(VI) occur only in black RhFg and yellow IrFg, formed by heating the metals with F2 under pressure and quenching the volatile products. Both RhFg and IrFg are octahedral monomers. The pentafluorides are made by direct combination of the elements (equation 22.100) or by reduction of MFg, and are moisture-sensitive (reaction 22.101) and very reactive. They are tetramers, structurally analogous to NbFs (22.5). 

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