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
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(a1g), ν2(ey). and (in some cases)ν5(t2g) 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 ᾱMX′, α‖′ and α⊥′ for [SbCl6]–, [TeCl6]2–, and [TeBr6]–2. The α‖′ values for TeIVX are 40–50% higher than those for SnIVX, from which it is deduced that the a1g* molecular orbital which accommodates the lone pair of s electrons in the case of TeIV is significantly involved in the Te–X bonding. Detailed excitation profiles of the ν(a1g) and ν(eg) 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.