Synthesis, characterisation and dynamic behavior of photoactive bipyridyl ruthenium(II)-nicotinamide complexes

The synthesis, characterization and dynamic behavior of three complexes, cis-[Ru(bPY)(2)(NA)CI][PF6] (1), cis-[Ru(bPY)(2)(NA)I][PF6] (2) and cis-[Ru(bpY)(2)(NA)(2)][PF6](2) (3), where bpy is 2,2'-bipyridine, NA is nicotinamide are reported. These were designed as potential photoactivated antibacterial agents. Their dynamic behavior in solution was explored using NMR to probe the presence of atropisomers. The data show that the NA ligand in the bis-NA complex 3 rotates freely at 298 K on the NMR timescale; however, NA rotation in the mono-Cl and mono-I complexes 1 and 2 is hindered at the same temperature. DFT calculations suggested that this hindered rotation is due to hydrogen bonding between the NA protons closest to the nitrogen of the pyridine ring and the halide ligand. Interestingly CI hinders rotation more than 1, which corresponds to hydrogen bonding ability. Such dynamic behavior may influence the recognition of polypyridyl ruthenium drugs by biological targets. (C) 2016 The Authors. Published by Elsevier B.V.