Near infra-red emission from a mer-Ru(II) complex: consequences of strong σ-donation from a neutral, flexible ligand with dual binding modes

A rare example of dual coordination modes by a novel tridentate ligand gives rise to unique fac-and mer-Ru-(II/III) complexes. The mer-Ru-II-complex displays the farthest red-shift of a triplet metal-to-ligand charge transfer ((MLCT)-M-3) emission with a tridentate ligand for a mononuclear complex. This observation is a consequence of large bite angle and strong sigma-donation by the ligand, the combined effect of which helps to separate the energy of the (MLCT)-M-3 and (MC)-M-3 states.