Studies of metal halides. III. Far-infrared spectra of chromium(III) and molybdenum(III) complex halides of formula A₃M₂X₉ and A₃MX₆

Abstract

Far-infrared spectra are reported for compounds of formula A₃M₂X₉, with M = Cr, Mo; X = Cl, Br; A = univalent cations, for the region 400-200 cm ^-1. Assignments for metal-terminal halogen and metal-bridging halogen stretching vibrations in the binuclear anion are proposed. Data on several related mono-nuclear hexahalo complexes are included for comparison. An explanation is offered for differences in the spectral features of the series of compounds in terms of distortions of the binuclear anion which arise from cation-anion interaction in the crystal lattice.