Vibrational spectra and quantum chemical investigations of stoichiometric anions in the series Tl2P2S6−Se and Ag2P2S6−Se with x=0–6. Evidence of the hexaselenidometadiphosphate anion, P2Se62−

Abstract

Abstract Vibrational spectra are presented for Tl 2 P 2 S 6− x Se x and Ag 2 P 2 S 6− x Se x ( x =0–6) reaction mixtures. Reaction charges with high selenium contents gave glassy products in which the main building units appear to be the hexaselenidometadiphosphate anion, P 2 Se 6 2− . For intermediate x values mixed thio–seleno–metadiphosphates are formed. Geometry and equilibrium energy are calculated and the vibrational spectrum of the P 2 Se 6 2− anion is well modelled by ab initio quantum chemical calculations. For the probably microcrystalline Tl 2 P 2 S 6− x Se x series, Se seems to first enter the terminal positions of the anions. According to the calculations, bridged selenium and terminal sulfur are favored in mixed P 2 S 6− x Se x 2− anions, and the spectra seem to verify this for the Ag 2 P 2 S 6− x Se x series. No evidence for monomeric PSe 3 − was found.