A CNDO/INDO crystal orbital model for transition metal polymers of the 3d series?the band structure of nickel(II)glyoximate

Abstract

The band structure of nickel(II)glyoximate has been investigated by means of an INDO crystal orbital formalism based on the tight-binding approximation. Calculations have been performed for unit cell dimensions of 3.223 A which corresponds to the geometry of the partially oxidized chain and of 3.547 A for the unoxidized polymer. The convergence of the lattice sums has been studied. It is shown that resonance and classical electrostatic integrals lead to a fast convergence while the exchange contributions are only slowly reduced with increasing intercell separation. The rotational profile of the title compound shows a pronounced minimum for the staggered 90 ° conformation; this is in line with experimental X-ray data. The conformation of the low-dimensional system is determined by the maximization of stabilizing intercell energies. The intracell stabilization is largest for an orientation where the intercell coupling is most inefficient (α = 50 °−60 °). Ligand π and lone-pair bands are predicted on top of the various Ni bands in the INDO band structure calculations. This sequence is conserved even if the creation of localized 3d states with trapped valences upon partial oxidation is considered. The ground state of the partially oxidized polymer corresponds to a system where charge density from the ligand framework has been removed leading to a typical organic metal or semimetal. The computational results are compared with experimental observations.