A vibrational study of various K2PdCl(4-x)Br(x) solid solutions

Infrared and Raman vibrational spectra (700-30 cm(-1)) have been recorded on various K2PdCl(4-x)Br(x) (0 < or = x < or = 4) powdered samples at 300 K, including both K2PdCl4 and K2PdBr4 compounds and ten solid solutions with a bromide content varying from 5-95%. Characteristic variations of the sectra clearly demonstrate a wide domain of existence of the solid solutions and the only possible additional existence, due to no IR-Raman coincidence, of the 'trans' planar PdCl4Br2 centrosymmetric anion. A comparison of the vibrational data with results of valence force field calculations allows us to characterize this new anion, in Raman by two signals at 286 and 225 cm(-1) (v sym., Ag, PdCl2 and PdBr2, respectively), in Infrared by not only the two bands at 309 and 200 cm(-1) (v asym. B3u + B2u, of PdCl2 and PdBr2) but also intense deformation modes in the 178-140 cm(-1) wavenumber range. These results suggest slight modifications in the internal f(Pd-Cl) and f(Pd-Br) force constans on going from the PdCl4(2-) or PdBr4(2-) anions to the 'trans' PdCl2Br2(2-) anonic species.