Bonding in low-coordinate complexes : what, if anything, is special?

Abstract

To contribute to the fundamental picture of the electronic structure of low-coordinate transition metal complexes, we have carried out a series of DFT studies on mono-imido and nitrosyl complexes for different metal ions (Mn^II/III, Fe^II/III/IV, Co^II/III) and different systems of basal ligands. These studies reveal striking similarities of the electronic structure for these systems. The distinction of bent versus linear NO units is attributed to the ranking of the dz2 and dxz/yz parentage MOs relative to each other. Without a ligand trans to the NO group, the antibonding metal dz2- NO σ orbital interaction is lessened by mixing in metal pz, causing the MO to shift away from the NO ligand. This exact same orbital interaction appears to explain the existence of middle to late first-row transition metal imido complexes.