A vibrational study of various K2PdCl4-xBrx solid solutions

Infrared and Raman vibrational spectra (700-30 cm(-1)) have been recorded o n various K2PdCl4-xBrx (0 less than or equal to x less than or equal to 4) powdered samples at 300 K, including both K2PdCl4 and K2PdBr4 compounds and ten solid solutions with a bromide content varying from 5-95%. Characteris tic 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 ani on. A comparison of the vibrational data with results of valence force fiel d calculations allows us to characterize this new anion, in Raman by two si gnals 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. B-3u + B -2n, 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 PdCl42- or PdBr42- anions to the 'trans' PdCl2Br22- anonic species. (C) 2000 Elsevier Science B.V. All rights reserved.