An Effective Core Potential ab Initio Study of Electronic Structure and Bandwidth-Charge Transport Relationships in Low-Dimensional, Partially Oxidized Palladium Glyoximates

Ab initio calculations on cofacial dimers of palladium bis(glyoximates) are reported and are used to rationalize the temperature-dependent conductivity of the low-dimensional, partially-oxidized material Pd(dpg)₂^0.20+(I₅⁻)_0.20 (dpg = diphenylglyoximato). The band structure near the Fermi level is dominated by two bands, of b_3g and a_u symmetry in the dimer, that arise from the ligand π orbitais. Near the observed (dpg)₂Pd-Pd(dpg)₂ staggering angle (90°), the b_3g bandwidth is zero, and the a_u band exhibits sharp variations with librational (twist) motion about the intermolecular Pd-Pd vector. This in turn, combined with the narrow bandwidth (calculated to be ~0.60 eV in a tight-binding model) implies that the electronic states are localized and that the material should be a hopping semiconductor rather than a molecular metal, in agreement with experiment.