Source function description of metal–metal bonding in d-block organometallic compounds

Abstract

The Source Function (SF) analysis is applied to a set of saturated [M₂(CO)_x, M = Mn, Fe, Co, Ni, x = 10, 9, 8, 7] and unsaturated [Co₂(CO)_x, x = 8–5] binuclear 3d metal carbonyls, and to the M₂(formamidinate)₄ (M = Nb, Mo, Tc, Ru, Rh, and Pd) binuclear 4d metal complexes, using ab initio electron densities. A description of the metal–metal (M–M) bonding closely related to that provided by the localization/delocalization indices is afforded. The agreement persists even when the M–M bond is lacking and the internuclear M–M midpoint is taken as a reference point for evaluating the SF contributions. However, use of the local form of the SF unveils interesting differences in how the charge density originates at the M–M midpoint when the system is metal–metal bonded or not. Most of the topological indices conventionally adopted to describe M–M bonds fail in reproducing the expected chemical trends for the set of investigated systems, with the adimensional |V_b|/G_b ratio and the ∇²ρ_b value being particularly inadequate.