A DFT based assessment of coordination modes of the bis(1-methyl-2-imidazolyl)glyoxal ligand in mononuclear and dinuclear complexes

The ligand bis(1-methyl-2-imidazolyl)glyoxal (big) was studied by DFT with respect to energy minimum conformations in the neutral, cation and anion radical states. Coordination alternatives involving chelate rings of different size were calculated for the partly experimentally accessible mononuclear complexes of big with [AuCl2]+, [Rh(C5R5)Cl]+ and Re(CO)3Cl. Comparative DFT calculations of various coordination modes for mononuclear, homodinuclear and heterodinuclear complexes of the potentially tetradentate big ligand reveal a preference for seven-membered chelate rings in the mononuclear species and for edge-sharing six-membered chelate rings with anti configuration of the metal-chloride bonds for the dinuclear systems, supporting the experimental evidence obtained through spectroscopic and electrochemical studies of {(μ-big)[Re(CO)3Cl]2}.