Temperature dependence of infrared spectra of [Pd(dddt) (2)](2)AuBr2 and [Pd(dddt)(2)](2)SbF6 salts

Polarised reflectance and transmittance spectra of two isostructural charge -transfer salts [Pd(dddt)(2)](2)AuBr2 and [Pd(dddt)(2)](2)SbF6 (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate ligand) have been measured over th e frequency range 650-6500 cm(-1) as a function of temperature (90-300 K). Additionally, powder absorption spectra of both compounds have been studied in the region 400-40000 cm(-1) at room temperature. Plasma-edge-like dispe rsion observed in the reflectance spectra is analysed in terms of a Drude-L orentz model. A metal-insulator phase transition in [Pd(dddt)(2)](2)SbF6 at T approximate to 200 K is observed in the spectra and discussed. Temperatu re dependence of vibrational bands, especially those related to the couplin g of electrons with the totally symmetric vibrations of Pd(dddt)(2), is inv estigated. (C) 2000 Elsevier Science S.A. All rights reserved.