The band structure of bis-(1,2-benzoquinonedioximato)-nickel(II)-a crystal orbital approach based on the INDO approximation

The band structure of bis-(1,2-benzoquinonedioximato)nickel(II), Ni(bqd) 2 , is investigated by means of crystal orbital calculations based on a semiempirical INDO model. The nature of the metal-metal interaction in the stack as well as the intercell coupling between the 3d centre and the ligand atoms is analysed in detail. There is no evidence for an attractive Ni-Ni interaction; stabilising contributions in the intercell potential are predicted for the coupling between the positivated Ni centres and ligand atoms with a surplus of charge. The net interaction energy is decomposed into increments of physical significance. A large number of ligand bands is predicted on top of the Ni 3d bands; strong metal-ligand mixing in the latter band set leads to significantly reduced 3d amplitudes in most of the transition metal bands (3d z2 , 3d xz , 3d yz ). The partially oxidised Ni(bqd) 2 polymers belong to the class of organic metals, the charge transport is due to ligand functions of lone-pair and pi character.