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)], [(CH 3 CN)(CO) 3 Re(μ-BBDB)Re–(CO) 3 (CH 3 CN)] 2+ , [(bpy) 2 Ru-(μ-BBDB)Ru(bpy) 2 ] 4+ , [(NH 3 ) 4 Ru(μ-BBDB)–Ru(NH 3 ) 4 ] 4+ (bpy = 2,2′-bipyridine) and complexes of Ru with 4-Me-4′-CO 2 H-bpy (=4-methyl-4′-carboxylic acid-2,2′-bipyridine) – the hydrolyzed derivative of BBDB – of formulae: [(Ru(4-Me-4′-CO 2 H-bpy)(bpy) 2 ] 2+ and [Ru(4-Me-4′-CO 2 H-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.