Low frequency vibrational spectra of bromo‐and iodoantimonates

The Raman and far‐infrared spectra of a dozen antimony halide complexes of formula SbX₆⁻³, SbX₅⁻², Sb₂X₉⁻³ and SbX₄⁻¹ have been recorded and analyzed for X = Br and I. The stretching frequencies for the bromo complexes range from about 135 to 220 cm⁻¹ for external bonds and from about 110 to 130 cm⁻¹ for bridging bonds. For the iodo complexes the ranges observed are 138–174 cm⁻¹ (external) and 87–127 cm⁻¹ (bridging). Approximate force constants were calculated for the anions and these were compared to values previously determined for halobismuthates. In general, the ordering of the force constants was found to be SbBr>SbI˜BiBr>BiI. As was found for the bismuth complexes, the stretching force constants were greatest for bonds in the anions in which the largest number of other bonds were to bridging halogens.