Rhodium and ruthenium tetracarboxylate nitrosyl complexes: Electronic structure and metal-metal bond

The electronic structure of the tetracarboxylates M2(μ-O2CH)4, M2(μ-O2CH)4(L)2 (M = Ru, Rh; L = H2O, NO) was analyzed by the density functional theory with full geometry optimization. The inclusion of nitrogen oxide orbitals into the molecular orbitals forming the metal-metal bond affects all of the main characteristics of this bond and the concomitant properties. In the case of rhodium tetracarboxylates, one can consider destruction of the Rh-Rh covalent σ-bond and reorientation of two electrons from the internal region of the Rh2(μ-O2CH)4 core to the outside, toward the axial ligands to give Rh-N covalent bonds. The axial coordination of nitrogen oxide in Ru2(μ-O2CR)4 is accompanied by destruction of the metal-metal π-bond.