Electronic Structure of Tetracoordinate Transition-Metal Complexes. 2. Comparative Theoretical ab Initio/Hartree-Fock-Slater and UV-Photoelectron Spectroscopic Studies of Building Blocks for Low-Dimensional Conductors: Glyoximate Complexes of Palladium(II) and Platinum(II)

This contribution presents an integrated experimental He I/He II UV photoelectron spectroscopic and theoretical ab initio pseudopotential and first-principles local exchange DV-Xα approach to understanding the electronic structure of the bis(glyoximato) (gly) complexes of Pd(II) and Pt(II). Theoretical results include evaluation of reorganization energies in the ion state to interpret PE spectroscopic data as well as relativistic corrections to account for the effect of the heavy atom in Pt(gly)₂. These results provide convincing descriptions of the metal-ligand bonding. The bonding involves almost all of the upper filled molecular orbitals (σ and π) of the ligand cluster. In particular, interactions with orbitals of a symmetry involve empty ndxy and (n + 1)s metal orbitals and result in an appreciable ligand-to-metal charge transfer. This effect is especially important in the case of the Pt complexes and raises the energies of metal d subshells. Detailed assignments of the UV PE spectra are proposed on the basis of both theoretical results (ASCF and TSIE calculations) and He I/He II intensity changes in the PE spectra. The present results argue that charge transport in low-dimensional, partially oxidized [Pd(gly)₂ ^+ρ]_nsystems will occur via bands that are significantly ligand π-electron in character (as in Ni(Pc)^+ρsalts). In contrast, transport in the corresponding [Pd(gly)₂ ^+ρ]_nsystems is likely to be via a largely metal-based band structure (as in conductive tetracyanoplatinate salts).