Nature of the bond, reduction potential, and solvation properties of ruthenium nitrosyl complexes of the type trans‐[Ru(NH₃)₄(L)(NO)]^2+/3+ and [Ru(salen)(L)(NO)]^2+/3+ in different charge and spin states

Abstract

In this work, we present a systematic study of the nature of the RuNO bond, reduction potential, and behavior in the solution of several ruthenium nitrosyl complexes of the type trans‐[Ru(NH3)4(L)(NO)]2+/3+ (L = Cl, H2O, NH3, OH, py = pyridine, POEt3 = triethylphosphite, TVP = trivinyl phosphite) and [Ru(salen)(L)(NO)]2+/3+ (L = Cl, H2O) in different charge and spin states. We employed density functional theory, complete active space self‐consistent field, the quantum theory of atoms in molecules, charge decomposition analysis, and Monte Carlo statistical simulation in aqueous solution to investigate how the different ligands on the coordination sphere of the ruthenium atom can affect the nature of the RuNO bond and, therefore, its reactivity, reduction potential, and solvation properties. The nature of the RuNO bond varies significantly between the singlet, doublet, and triplet electronic states of these complexes, in part due to the change in the coordination mode of the NO ligand and also due to the electron correlation effects along the RuNO bond that changes drastically. For all complexes studied, the RuNO bond shows some intriguing characteristics, such as large kinetic energy density and considerable amount of electron localization between the atoms, besides high multiconfigurational character, with a significant contribution from the RuIIINO0 configuration. In addition, for all the complexes investigated, the NO ligand does not interact with the solvent through hydrogen bonds, making this group accessible for chemical reactions in solution. Another important finding was that some of the RuIIINO compounds can be reduced by biological reducing agents in the singlet ground state, while all of them have high reduction potentials in the triplet excited state, making them suitable candidates for the photorelease of nitric oxide.