Spectroscopic, electrochemical and computational studies of rhenium(I) and ruthenium(II) complexes incorporating the novel tetradentate ligand 1,4-bis(4-(4′-methyl)-2,2′-bipyridyl)-2,3-diaza-1,3-butadiene (BBDB) and its derivatives.

Abstract: The novel tetradentate ligand 1,4-bis(4-(4′-methyl)-2,2′-bipyridyl)-2,3-diaza-1,3-butadiene (BBDB) was synthesized and characterized by spectroscopic techniques. New complexes of Re and Ru of formulae: [Re(BBDB)(CO)3(Cl)], [(CH3CN)(CO)3Re(μ-BBDB)Re–(CO)3(CH3CN)]2+, [(bpy)2Ru-(μ-BBDB)Ru(bpy)2]4+, [(NH3)4Ru(μ-BBDB)–Ru(NH3)4]4+ (bpy=2,2′-bipyridine) and complexes of Ru with 4-Me-4′-CO2H-bpy (=4-methyl-4′-carboxylic acid-2,2′-bipyridine) – the hydrolyzed derivative of BBDB – of formulae: [(Ru(4-Me-4′-CO2H-bpy)(bpy)2]2+ and [Ru(4-Me-4′-CO2H-bpy)(CN)4]2− were prepared and characterized by spectroscopic, electrochemical and computational techniques. The disclosed enhanced electronic coupling in the mixed-valent complex with ruthenium ammines can be explained by the electronic delocalization imposed by the C N N C backbone. DFT and TD-DFT calculations can predict the optical properties and electronic structures of the reported complexes and comparisons with calculations performed on previously reported complexes with 4-pyridinaldazine can account for their photophysical behaviour. [Copyright &y& Elsevier]