A study of the shapes of the isoelectronic species antimony pentafluoride (monomer), tellurium tetrafluoride oxide (dimer), and iodine trifluoride dioxide (polymer)

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Abstract
The vibrational spectrum of (assumed) monomeric antimony pentafluoride can be assigned acceptably on the basis of a D3h model. In agreement with earlier work tellurium tetrafluoride oxide dimer is found to be strongly oxygen bridged, in sharp contrast to tungsten tetrafluoride oxide which is weakly fluorine bridged in the solid state but readily dissociates to a square pyramidal monomer. Despite variable-temperature i.r. and Raman studies no trace of reversible equilibria involving a terminal Te–O bond was detected, iodine trifluoride dioxide was found to be polymeric. On the basis of physical studies including n.m.r. and vibrational spectra together with molecular-weight studies it is likely that the principal constituent of the vapour is a centrosymmetric oxygen bridged dimer with ‘axial’ fluorines. The similarity of the Raman spectra of the solid, melt, and gas strongly suggests the same basic unit to be present in all states. The interesting comparison between the oxygen bridging of fluoride oxides of the non-transition elements compared with the fluorine bridging of the fluoride oxides of the transition elements is discussed.

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