Correlating Magnetic Exchange in Dinuclear Bis(phenolate)-Bridged Complexes: A Computational Perspective

Density functional theory (DFT) calculations were performed to analyse the magnetic properties of dinuclear Ni-Ni and Cu-Cu bis(phenolate)-bridged complexes with two anti-ferromagnetically-coupled metals. The estimated coupling constants J are -384.8 and -375.3 cm(-1) for the two Cu complexes and -85.7 cm(-1) for the Ni complex, which are consistent with the experimental values. Analysis of overlap integral can explain the difference in the coupling J between Ni and Cu complexes: Two d(x2-y2) orbitals of the copper complexes are located on the same plane as that of a phenolate ligand, and therefore produce the strong J coupling, whereas those of the nickel complex are tilted from the plane of phenolate ligand because of asymmetric environment around Ni atom, and produce moderate J coupling. We also examined the dependences of magnetic interaction in terms of several important geometrical parameters. The M-O-M bond angle is the key parameter for antiferro-ferromagnetic transition, which is consistent with previous studies for the other complexes. Also, increasing the M-O-O-M dihedral angle, decreasing the M-O-M bond angle and large hinge distortions on these complexes effectively enhance the ferromagnetic exchange, which is a desired condition for a better molecular magnet.