Electronic structure of triangular trigold(I) complexes. A theoretical study

Triangular trigold(I) complexes have been synthesized and characterized by several authors. These molecules have linear two-coordinated gold(I) centers connected by bridging ligands to form nine-membered rings. Although this type of molecules have been known for more than 20 years, some remarkable properties have attracted new interest. Au3(CH3NCOCH3)3 shows solvoluminescence, supramolecular association and some (μ-pz-N,N)3Au3 form mesophases with hexagonal columnar structures with weak dimer formation. In this work we study the electronic structure of these molecules. We also include [Au(μ-N3,C2-bzim)]3 and [2-pyridyl-Au]3. Calculations were done at B3LYP level with 6-31++G basis for all atoms except Au where LAN2LDZ was used. Geometry optimization shows that all molecules are flat and highly symmetric. For molecules 1 and 4 the LUMO is mainly located on the rings and the HOMO main contributions are from the Au atoms. In molecules 2 and 3 the LUMO main contributions are from the gold's. An electronic delocalization similar to aromaticity is found in the nine-member ring of all compounds. This effect is studied with the NICS index.