Arene ruthenium complexes incorporating immine/azine hybrid-chelating N–N′ donor ligands: synthetic, spectral, structural aspects and DFT studies

New series of mono and binuclear arene ruthenium complexes [{(η6-arene)RuCl(L)}]+ and [{(η6-arene)RuCl}2(μ-L)2]2+ (arene=benzene, p-cymene or hexamethylbenzene), {L=pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)-aldimine (pbp) and p-bi-phenylene-bis(picoline)-aldimine (bbp)} are reported. The complexes have been fully characterized and molecular structure of the representative mononuclear complex [(η6-C6Me6)RuCl(paa)]BF4 (1), binuclear complexes [{(η6-C10H14)RuCl}2(μ-paa)](BF4)2 (3) and [{(η6-C10H14)RuCl}2(μ-pbp)](BF4)2 (6) have been determined by single crystal X-ray diffraction analyses. Single crystal X-ray structure determination revealed that in the binuclear complexes the [(η6-C10H14)RuCl]+ units are trans disposed. Further, the crystal packing in the complexes 1, 3 and 6 is stabilized by C–H⋯X type (X=Cl, F) inter, intramolecular hydrogen bonding and π–π stacking (3). To explore the ambiguous nature of the bonding between pyridine-2-carbaldehyde azine (paa) with ruthenium containing units [(η6-arene)RuCl]+, DFT/B3LYP calculations have been performed on the complexes [(η6-arene)RuCl(paa)]+ (arene=C6H6, I; C6Me6, II; C10H14, III).