Polymetallic complexes: structure, reactivity and properties

C. Gourlaouen, V. Robert, E. Fromager

In principle, interaction between cations should only by repulsive. However, in many experimental structures, inter-cation distances are smaller than the sum of ionic radii. These complexes, generally composed of electron rich cation from column 10 (NiII, PdII) to 13 (TlI), exhibit very interesting optic, magnetic or catalytic properties. Two main research activities are developed in our group.

The first one consists in the description of closed-shell cation interaction called metallophilic interactions. These particular bonds derive from electron correlation and are reinforced by relativistic effects as for Au+ cations. Theoretical methods able to described both static (MCSCF) and dynamic (DFT, CAPST2, MP2…) correlation are required to properly model these species. However, the large size of these systems makes the calculation computationally very resource demanding. This motivates the development of hybrid MCSCF-DFT and post MCSCF-DFT methods for describing metallic interactions. The main idea is to combine the best of DFT and (post-)MSCF approaches in terms of accuracy and computational cost. We want to highlight the specific interaction between the cations and to determine the role played by other factors on the bond length and binding energy. This is done by modifying the cation coordination sphere to control donation, steric effects or electrostatic interactions.

Our second research interest is the extension of the previous studies to metal string complexes. These species consist of metallic cation linear strings in which transition metals are stabilized by rigid ligands as polypyridylamid or polynaphtyridylamid. The presence of open-shells is the source of interesting magnetic properties, where different behaviours are generated from the multicenter architectures. This implies the treatment of electron correlation in a multi-reference scheme.

We search to decipher the nature of metal-metal interactions. This work requires the use of new methods supported by those developed in our laboratory to treat the electron correlation for such complex species. The use of topological analysis (ELF: Electron Localization Function) and of binding energy decomposition (CSOV and RVS) provide further information on this interaction and its sensitivity to the chemical and physical environment.