Electron correlation in weakly coupled binuclear transition metal compounds: Cyclopentadienyl-allyl-cyclobutadiene-dinickel

The Hartree—Fock (HF) instabilities of the binuclear 3d complex cyclobutadiene-allyl-cyclobutadiene-dinickel (1) have been investigated by means of a semi-empirical INDO approach. It is demonstrated that the HF solution is unstable with respect to singlet, non-singlet and complex variations. The MO fluctuation leading to the singlet instability is predominantly localized in the region of Ni₂ and the four-membered ring. The lowest eigenvalue of the triplet instability corresponds to a spin decoupling between both Ni centers. Consequences arising from HF instabilities in binuclear transition metal compounds for the comparison between theoretical model calculations and experimental data (e.g. vertical ionization potentials, geometries, geometrical preferences, transport properties) are shortly discussed.