Vibrational spectroscopy at very high pressures. Part V. Far-infrared spectra of inert pair hexahalogeno-complexes

Abstract

Far-i.r. spectra of salts of [SeX₆]^2–(X = Cl or Br), and [TeX₆]^2–(X = Cl, Br, or I), are reported for pressures up to 40 kbar. All observed bands show blue shifts but the most dramatic effects are exhibited by the ν₄ bending modes of the anions. For some compounds ν₄ is absent at ambient pressure but appears at increased pressure and exhibits a large blue shift, but other compounds which have ν₄ initially lose it at elevated pressure. These effects are accounted for on the basis of an anion–cation bonding scheme which allows a pressure-dependent delocalisation of inert-pair electrons throughout the lattice.