The Nature of the Ru−NO Bond in Ruthenium Tetraammine Nitrosyl Complexes

Abstract

Quantum chemical calculations at the DFT level have been carried out for trans-[RuII(NH3)4(L)NO]q and trans-[RuII(NH3)4(L)NO]q-1 complexes, where L = NH3, Cl-, and H2O. The equilibrium geometries and the vibrational frequencies are reported not only for the ground state (GS) but also for light-induced metastable states MS1 and MS2. The nature of the Ru−NO+ and Ru−NOo bonds has been investigated by means of the energy decomposition analysis (EDA). The nature of the Ru−NO bond has been analyzed for the three states GS, MS1, and MS2, considering two different situations: before and after one-electron reduction. The results suggest that not only the orbital term but also the ΔEPauli term is responsible for weakening of the RuII−NOo bond, the ΔEPauli term increasing in comparison with the RuII−NO+ bonds, thus making the NOo ligand more susceptible to dissociation in comparison with NO+. Calculations of the RuIII−NOo species show that in this case the bonds are mainly covalent, but the electrostatic stabilization also plays an important role. Among the orbital interactions, the π-back-donation is the most important term.