Intensity studies on the Raman-active fundamentals of hexahalogeno-anions of antimony(V) and tellurium(IV); the calculation of parallel and perpendicular bond-polarisability derivatives and Raman-band excitation profiles of the hexabromotellurate(IV) ion

Abstract

The Raman spectra of solutions (generally acetonitrile) of the ions [SbCl₆]^–, [TeCl₆]^2–, and [TeBr₆]^2– have been recorded, and accurate values for the frequencies of the ν₁(a_1g), ν₂(e_y). and (in some cases)ν₅(t_2g) fundamentals are reported. The intensities of the fundamentals of each ion have been measured using the rotating-sample technique with 4–6 different exciting lines and they are reported by reference to the 935-cm^–1 line of the perchlorate ion as internal standard. The intensity results, which are treated in terms of the pre-resonance Raman effect, have been extrapolated to zero exciting frequency to yield values for the polarisability derivatives ᾱ_MX′, α_‖′ and α_⊥′ for [SbCl₆]^–, [TeCl₆]^2–, and [TeBr₆]^–2. The α_‖′ values for Te^IVX are 40–50% higher than those for Sn^IVX, from which it is deduced that the a_1g* molecular orbital which accommodates the lone pair of s electrons in the case of Te^IV is significantly involved in the Te–X bonding. Detailed excitation profiles of the ν(a_1g) and ν(e_g) fundamentals of [TeBr₆]^2– in acetonitrile have been obtained from dye- and ion-laser measurements with 10 different exciting lines, and the results are discussed with reference to the electronic spectrum of the ion in the 450–650 nm region.