Ruthenium complexes with 2,2′-, 2,4′- and 4,4′-bipyridine ligands: The role of bipyridine coordination modes and halide ligands

Ruthenium complexes with 2,4′-bipyridine and 4,4′-bipyridine ligands, [(2,4′-bpy)RuCl2(CO)3] and [(4,4′-bpy)(RuCl2(CO)3)2], were synthesised and structurally characterised. These new complexes were compared to the well-known ruthenium compound [(2,2′-bpy)RuCl2(CO)2] by computational and experimental methods to investigate the effects of the chelating and non-chelating coordination modes of the bipyridine ligand. The stabilisation effect of the chelating 2,2′-bipyridine structure was observed. In addition to bipyridine coordination studies, theoretical studies on the effect on energy levels of changes of halide ligands in the coordination environment for ruthenium complexes were carried out showing that halides possess a significant role in the HOMO–LUMO energy gap. The ligand substitution changed especially the HOMO levels while leaving LUMOs almost intact. The computational approach was found to be a valuable aid in the design and tuning the electronic properties of ruthenium bipyridines.