Infrared, Raman and resonance Raman spectra of the solid nickel(II) thiophosphate compound (PPh4)3 [(NiPS4)3] and force constants in the trinickel [Ni3P3S12]3− cyclic anion

Abstract

The UV–visible (350–900 nm), infrared and Raman (30–800 cm−1) spectra of a new transition metal thiophosphate solid compound, (PPh4)3 [(NiPS4)3], were analyzed using powder samples. Electronic transitions of the 1F2 1A1 type originating in the (PS4)3− groups were detected from visible absorbance measurements in the 440–520 nm range and most of the expected infrared and Raman vibrational modes of the trimetallic ring anion [Ni3P3S12]3− were observed in the 600–30 cm−1 region. Also, resonance Raman spectra were recorded using exciting radiation of several wavelengths in the 680–450 nm range and the Raman excitation profiles of several fundamentals were established: they all peak near 488 nm and exhibit the strongest enhancements for totally symmetric and non-totally symmetric stretching and bending modes of (NiS4) groups. It is therefore concluded that several ligand to metal charge-transfer electronic transitions are overlapped and involved in vibronic coupling mechanisms. Furthermore, the vibrational assignments were checked by a valence force field calculation for an isolated [Ni3P3S12]3− anion of C3v symmetry. The potential energy distributions and mean squared vibrational amplitudes revealed strong ν(Ni–S) and δ(S–P–S) couplings and relatively high ν(Ni–S) stretching modes at near 310 cm−1. Compared with results in the one-dimensional KNiPS4 compound containing infinite anionic chains [NiPS4]−, one notes a force constant increase on the P—S exocyclic (µ1) bonds, no change on the bridged (µ2 and µ3) P—S bonds and a slight increase in the Ni–S stretching force constants varying from 75 to 85 N m−1 in accordance with a localized ligand to metal charge-transfer mechanism. Hence a comparison of the induced Raman scattering processes in the (PPh4)3 [(NiPS4)3] and KNiPS4 solid compounds shows that the ligand to metal charge transfers and the crystal field effects have a strong influence on the vibrational properties in these thiophosphate compounds. Copyright © 1999 John Wiley & Sons, Ltd.