METAL PHTHALOCYANINE GROUND-STATES - COVALENCE AND ABINITIO CALCULATION OF SPIN AND CHARGE-DENSITIES

Ab initio UHFS DV-X-alpha calculations of the low-lying states of manganese, iron, and cobalt phthalocyanines have been carried out with basis sets corresponding to about "double-zeta" quality. Comparison with experimental spin and charge densities on beta-polymorph crystals shows the ground states to be 4E(g) 3E(g) (or less likely 3B2g), and 2A1g, respectively. The molecules are highly covalent, with sigma donation into 3d(x2y-y2) of ca. 0.7 e and pi back-donation into the macrocycle of ca. 1 e from d(xzyz), with the other 3d orbitals fairly ionic in character. The pi back-donation differs strongly between "up" and "down" spin, the up spin being mostly ionically localized in metal 3d(xzyz) orbitals whereas the down spin is strongly covalently delocalized onto the macrocycle. This large differential covalence appears in experiment as well as the calculation. Such covalence is compatible with ESR, magnetic and Mossbauer data on the crystals. Consequently, the assignment of ground state with ionic ligand field models can be misleading. The 3d dominated orbitals lie in the order 3d(x2-y2) >> 3d(z2) > 3d(xy) approximately 3d(xzyz) with up-spin members lower in energy than down-spin ones, giving the observed ground states. The closeness of the 3d(xy) and 3d(xzyz) down-spin orbitals in the calculation for FePc suggests that the contribution of 3B2g and 3E(g) in the spin-orbit mixed ground state may vary greatly depending on small changes in axial ligation. This means small changes in such ligation can produce changes in both spin and charge populations on metal and Pc of about 1 e.