Solid state phase transitions in linear transition metal polymers: M-M VS. M-L-M modification in bisglyoximato nickel(II)

Abstract

Abstract The band structure of bisglyoximato nickel(II) 1 , has been studied by means of crystal orbital (CO) calculations based on the tight-binding approximation as a function of the angle between the stacking axis and the mean molecular plane of the bisglyoximato ligand. The M-M phase of 1 is characterized by an angle of 90° (Δα = 0°) between the one-dimensional (1D) axis and the π plane of the organic fragments. The molecular planes of the glyoximato polymer are inclined to the 1D axis by an angle that differs from 90° in the M-L-M phase where the shortest intercell contacts are found between the 3d center and ligand atoms. Computational framework for the investigation of this phase transition (M-M ⇹ M-L-M) is a semiempirical INDO CO model. The band gap of 1 is reduced with increasing slipping deformations Δα. The width of the valence band is not significantly modified by the solid state transformation while the conduction band is broadened. The nature of the “Ni 3d bands” is significantly influenced by the mutual orientation of the organic π layers. Correlations between Ni 3dσ and 3dδ states and interconversions between ligand and transition metal CO wave functions are predicted in the M-L-M phase for large deformations Δα. Pronounced intramolecular charge redistributions are predicted as a function of the slipping deformation in the 1D stack. The intercell interactions in the M-M phase are prevailingly determined by classical Coulomb potentials while a strong covalent metal-ligand coupling is encountered in the M-L-M modification of 1 .