Infrared, Raman, resonance Raman spectra and lattice dynamics calculations of the solid potassium(I) nickel(II) thiophosphate compound, KNiPS4

Abstract

Abstract The UV-visible (350–850 nm), infrared and Raman (20–700 cm−1) spectra of a new KNiPS4 solid compound have been analyzed using powder samples and crystalline platelets. From polarization measurements, the main electronic transition of 1F2←1A1 type due to the PS43− thiophosphate groups are localized in the 360–570 nm range and vibrational assignments for most of the fundamental modes are proposed. These assignments were checked by complete valence force field lattice dynamics calculations in the various symmetry blocks of the tetragonal crystal structure (D4h14). Potential energy distributions as well as mean squared vibrational amplitude calculations have shown strong ν(NiS) and σ(SPS) couplings in the (NiPS4)− structural chains and remarkably high ν(NiS) infrared frequencies. Furthermore, the resonance Raman spectra of single crystals and powder samples were recorded over a wide range (647.1-476.5 nm) of excitatiob wavelengths. This allowed to probe the nature of the broad electronic transition of the complex centered around 510 nm and responsible for KNiPS4 brown color. The Raman excitation profiles of several fundamentals and combination bands were thus established. Under resonance conditions, various crystalline components of A1g, B1g and B2g symmetry for the ν4(F2) or ν2(E) deformation modes of the PS43− groups are enhanced. No overtone progressions involving totally symmetric modes were observed but anomalously intense high-order combination bands were detected. It is thus concluded that adiabatic as well as non-adiabatic interactions must play a great role in the vibronically induced Raman scattering processes. Reasons for this peculiar behavior are discussed in relation to the X-ray crystal structure of the KNiPS4 compound. All the experimental results imply the presence of substantial site and factor group effects on the optical and vibronic properties of the thiophosphate anions.