SPIN AND CHARGE DENSITY IN Ni(NH3)4(NO2)2 AND THE CHEMICAL BONDING

Polarised neutron and X-ray diffraction experiments have been performed on Ni(NHj^CNC^) 2 t o study respectively the spin and charge distributions in the molecule. The results have been compared with an ab-initio M.O. calculation. 27 % of the spin is transferred to the ligand atoms by covalent interactions. A simple ligand field model, with four empirical parameters, agrees qualitatively, but not quantitatively with the combined spin and charge results. The U.H.F. ab-initio calculation results are also in broad agreement with the experiments, but correspond to a pood deal less covalency in the bonding. This emphasises the need to consider configuration interaction and/or a long range "crystal field" in describing bonding in crystalline transition metal compounds.