Theoretical studies on nitrido ruthenium (VI) porphyrin and high valent ruthenium nitrido derivatives of Keggin typical polyoxometalate ([PW11O39{Ru(VI)N}]4-): electronic structures and bonding features

Abstract

In the present paper, the electronic structures and bonding features between the ruthenium atom and nitrido ligand of known nitrido ruthenium (VI) porphyrin and hexavalent ruthenium nitrido derivative of Keggin typical polyoxometalate (POM) have been investigated by using density functional theory (DFT) calculations and natural bond orbital (NBO) analysis. The results show that the Keggin POM complex and porphyrin complex have the Ru[triple bond]N triple bond, the NBO calculations yield a nitrido ligand charge close to zero in both complexes because of the charge transfer from the rich-electron nitrido ligand to the ruthenium center. The molecular orbitals predict that the ruthenium porphyrin complex would generate oxidized species with no change in the oxidation state of the metal center; however, the ruthenium center of the POM complex would be oxidized in a one-electron-oxidation process because of the different HOMO character, and moreover, the spin unrestricted calculations confirm this prediction made by molecular orbital analysis. On the other hand, both complexes have the same reduced center, the RuN unit, and the one-electron-reduction process weakens the bonding interaction between the ruthenium atom and nitrido ligand for both complexes because the antibonding LUMO is occupied. Compared with the porphyrin complex, the POM complex possesses a higher RuN composition and lower energy pi* antibonding orbital according to gas-phase and solvent calculations.