This IBO also appears to be the major component of the Kohn-Sham HOMO (Figure ). Based on Natural Population Analysis (NPA) charges from NBO, the terminal hydride of 2a H 2 accumulates more negative charge (-0.47) than either H 1 (-0.05) or both hydride ligands of 1 (-0.14, -0.18), hinting at its increased nucleophilicity (vide infra). The heterometallic core of 2a is supported by further electrostatic interactions between atoms pairs. Independent gradient model based on Hirshfield partition of molecular density (IMGH) and non-covalent interaction plot (NCIPlot) analysis detect attractive interactions with non-negligible covalent character between the two metal fragments further supporting the (semi-)bridging nature of the CO and H 1 ligands. Analysis of the pairwise atomic contributions to the interfragment interaction given by IGHM analysis (δG atom %) in also supports the reduction in strength of the metal-metal bond in 2a cf. 1 (see SI).