Electronic structure of dimetallocene molecules: Dizincocene Zn₂(η⁵-C₅Me₅) ₂

The properties of the recently synthesised dizincocene Zn₂(η⁵-C₅Me₅) ₂ have been studied by ab initio calculations using plane wave based density functional theory. The calculated geometry agrees well with single crystal X-ray measurements. Every methyl group is similarly oriented with one CH bond pointed away from the core approximately in a plane containing the configuration axis. The C₅Me₅ ligand is dished outwards. The Zn-Zn axis is not quite perpendicular to or pointed exactly at the C₅ ring centers. The top and bottom C₅ rings are not parallel but tilted a few degrees with respect to each other. In the central Zn-Zn bond there is less charge, indicated by isometric total charge density surfaces, than between ligand and metal atom. This metal-metal bond has σ- and π-components with the σ-bond mainly s-, with small p_z- and d_z ²-components and the π-bond with p_x-, p_y-, d_zx-, d_yz-components. The π^*-lumo orbital is especially interesting because the excited state charge is confined to a disk-like shape because of Pauli repulsion from the methyl groups. The electron localization function (ELF) has distinctive features. In the region of the dizinc central bond, the valence basin has toroidal and central ellipsoid components (ELF > 0.5) found in the zincous dication Zn₂ ^{2 +}. The valence basins of the C-C bonds of the C₅ ring are displaced slightly parallel to the major axis away from the central region, this effect along with geometric dishing is tentatively assigned as due to a small change in hybridization of ring carbon atoms due to loss of aromaticity.