M⋯H–C interaction – Agostic or not: A comparison of phenyl- versus pyridyl-bridged transition metal dimers

Two transition metal complexes of 2,6-bis[N-(8-quinolyl)carbamoyl]pyridine (L1) and one of 2,6-bis[N-(8-quinolyl)carbamoyl]benzene (L2) were synthesized and structurally characterized. Nickel(II) and copper(II) complexes with L1 gave bifurcated-pyridine dimeric complexes (1 and 2). A copper(II) complex of L2 gave the dimeric complex, 3, in which the isophthaloyl C–H moieties of both ligands have short contacts with the pair of copper centers. Density functional theory calculations at the B3LYP/6-31G∗ and B97-D/6-31G∗ levels of theory offer strong supporting evidence that the Cu(II)⋯H–C interactions in 3 are best described as weak hydrogen bonds rather than agostic interactions.