Electronic structure and energy decomposition of binuclear transition metal complexes containing β-diketiminate and imido ligands: spin state and metal's nature effects

DFT calculations with full geometry optimization using BP86-D and OPBE functionals have been performed on series of [(BDI)M(NH)](2)(Bz) and [(BDI)M(NH)](2)(Tol) (M = Ti, V, Nb, Cr, Mn, Fe, Co, and Ni; BDI = beta-diketiminate; NH = imido group; Bz = benzene; and Tol = toluene) of various spin states (singlet S = 0, triplet S = 1, quintet S = 2, and singlet S = 0 of broken symmetry method). Depending on the metal nature and its electron count and the spin state, the six-membered ring in [(BDI)M(NH)](2)(Bz) and [(BDI)M(NH)](2)(Tol) adopts various hapticities that involve full or partial coordination, giving rise to a flat or a distorted ring, respectively. The NH2- imido group is linear or bent with respect to its sp or sp(2) hybridization acting as a six- or a four-electron donor, respectively. The (BDI)(-) anion is a bidentate ligand as a six-electron donor. The optimized geometries do not show direct metal-metal bonding and correspond to long separations. The optimized structures for Nb metal are comparable to the available experimental ones. The Ziegler-Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion, the steric interaction (electrostatic and Pauli), and the orbital interaction terms in the total bonding energy. The results showed that the interaction terms in all the studied complexes are governed by one third covalent and two thirds ionic characters, which are in agreement with the Delta E-elstat (electrostatic) and Delta E-orb (orbital) contributions, respectively, into the total attractive interaction (Delta E-elstat + Delta E-orb).