Experimental and theoretical characterization of the Zn-Zn bond in [Zn2(eta5-C5Me5)2]

The existence and characterization of a bond between the Zn atoms in the recently synthesized complex [Zn(2)(eta(5)-C(5)Me(5))(2)], as well as between Zn and ligand C atoms is firmly based on neutron diffraction and low-temperature X-ray synchrotron diffraction experiments. The multipolar analysis of the experimental electron density and its topological analysis by means of the 'Atoms in Molecules' (AIM) approach reveals details of the Zn-Zn bond, such as its open-shell intermediate character (the results are consistent with a typical metal-metal single bond), as well as many other topological properties of the compound. Experimental results are also compared with theoretical ab initio calculations of the DFT (density functional theory) and MP2 (Møller-Plesset perturbation theory) electron densities, giving a coherent view of the bonding in the complex. For instance, charges calculated from the AIM approach applied to the atomic basin of each Zn atom are, on average, +0.72 e from both the experimental and the theoretical electron density, showing a moderate charge transfer from the metal, confirmed by the calculated topological indexes.