Electronic structure and electron-molecular vibration interaction in dimerized [Pd(dddt)(2)](2)X (where X=AuBr2, SbF6, TeClx) salts studied by IR spectroscopy

Polarized reflectance spectra of three isostructural charge-transfer salts [Pd(dddt)(2)](2)X (where X=AuBr2, SbF6, TeClx,, x=5 or 6, and dddt=5,6-dihy dro-1,4-dithiin-2,3-dithiolate Ligand) have been measured in the frequency range 650 to 40 000 cm(-1) at room temperature. Moreover, we studied absorp tion spectra (400 to 40 000 cm(-1)) as well as Fourier transform near-infra red Raman spectra of [Pd(dddt)(2)](2)TeClx powders. All the compounds conta in, strongly dimerized Pd(dddt), stacks. The nature of electronic bands is discussed. A plasma-edge-like dispersion in [Pd(dddt)(2)](2)AuBr2 and [Pd(d ddt)(2)](2)SbF6 crystals is analyzed in terms of Drude-Lorentz model. The b and-structure parameters are determined by assuming a one-dimensional tight -binding model. Deviations between the experimental data and expectations o f a one-electron model suggest considerable contributions of electron-elect ron and electron-phonon interactions to the electronic structure of the mat erials. The coupling of electrons with the totally symmetric C=C vibrations of Pd(dddt), (a(g) modes) in [Pd(dddt)(2)](2)AuBr2 and [Pd(dddt)(2)](2)SbF 6 salts is discussed in terms of an isolated dimer model and the suitable e lectron-phonon coupling constants are determined. The origin of a, phonon m ode splitting is considered. [S0163-1829(99)06123-8].