Laser-Raman spectroscopic study of the vapour phase of NbCl5 and mixtures of NbCl5 and SnCl2

Abstract

Vapour-phase Raman spectra of NbCl₅ at temperatures between 418 and 580 K and of 1:1, 1:2 and 2:1 mixtures of NbCl₅ and SnCl₂ at temperatures between 359 and 676 K have been recorded. Several features have been observed in spectra from the mixtures which do not correspond to those known for the pure components and these vibrational bands have been assigned to the vapour-phase complex NbSnCl₇. Normal coordinate analysis has been carried out for the proposed structure of the complex. Complexation of the tow components is shown to enhance the volatility of NbCl₅ by a factor of 3.75 at 420 K. SnCl₂ is shown to be more volatile when complexed with NbCl₅ than in its pure phase. Predicted vibrational band wavenumbers from force constant calculations, combined with observed wavenumbers have been used to calculate values for the heat capacity, C^°_p, the enthalpy, H^°_T–H^°₂₉₈, and the entropy, S^°_T–S^°_O, of NbSnCl₇(g) from 0 to 6000 K.