Vibrational spectra of niobium and tantalum pentafluorides in the gas phase. The vapour density of niobium pentafluoride

Abstract

Molecular weight data obtained through mass spectrometry and vapour density measurements show that at lower temperatures gaseous niobium and tantalum pentafluorides contain polymers. The results suggest the presence of monomeric, dimeric, and trimeric species.

The Raman spectra of the gaseous pentafluorides as a function of temperature confirm that (reversible) dissociation occurs as the temperature is raised. The i.r. spectra of these two compounds in the gas phase at temperatures and pressures where there is extensive polymerisation are in agreement with the presence of octahedrally co-ordinated metal atoms with cis-fluorine bridges. The i.r. spectrum of molten niobium pentafluoride is closely related to that of the gas at lower temperatures and to that of the solid, which is known to be polymeric.