The UV-Visible (350-900 nm), infrared and Raman (30-800 cm -1 ) spectra of a new transition metal thiophosphate solid compound, KPdPS 4 , were analyzed using powder samples and single-crystal platelets. From polarized absorbance measurements, the main electronic transitions of the 1 F 2 1 A 1 type due to the (PS 4 ) 3-groups are localized in the 400-520 nm range and all the expected infrared vibrational modes were observed in the 600-30 cm -1 region; various polarized Raman measurements were also performed.
The vibrational assignments were then checked by complete valence force field lattice dynamics calculations in the different symmetry blocks of the tetragonal crystal structure (D 4h 14 ). Potential energy distributions and mean squared vibrational amplitude calculations revealed strong n(Pd-S) and d(S-P-S) couplings in the one-dimensional inorganic polymer anionic 1
1 [PdPS 4 ] -chains and remarkably high n(Pd-S) stretching modes near 350 cm -1 . Compared with results for the analogous Ni(II) compound, there was a significant increase in the M-S force constants, varying from 75 Nm -1 (Ni-S) to 90 Nm -1 (Pd-S) in accordance with the Pauling electronegativity scale. Furthermore, various resonance Raman spectra of micrometersized samples were recorded using a confocal microscope instrument in order to characterize not only the existence of chains having a distribution of length but also some Raman impurity bands coming from the dithiophosphate compound, K 4 Pd(PS 4 ) 2 . Also, resonance Raman spectra of powder samples were recorded using several exciting radiation wavelengths over the range 800-500 nm in order to probe the nature of the low-energy electronic transition at 658 nm; the Raman excitation profiles of several fundamentals were thus established and they demonstrate that both totally symmetric and non-totally symmetric stretching and bending modes of the PS 4 and PdS 4 groups are markedly enhanced. We therefore conclude that several ligand to metal charge-transfer electronic transitions are overlapped and involved in vibronic coupling mechanisms with higher energy bands. Finally, a comparison of the induced Raman scattering processes in the Cu 3 PS 4 , KNiPS 4 and KPdPS 4 solid compounds showed that the ligand to metal charge transfers and the crystal field effects have a strong influence on the optical and vibronic properties of these thiophosphate compounds.