Metastable states of ruthenium (II) nitrosyl complexes and comparison with [Fe(CN)5NO]2−

The properties of the [Ru(NH3)5NO]3+ and [Ru(CN)5NO]2− ions are investigated by density functional theory and compared with those of [Fe(CN)5NO]2−. DFT calculations show that the electronic ground-state potential surface of these nitrosyl complexes has local minima (metastable states) with oxygen-bonded NO (MS1), i.e., inverted from the usual N-bonded species (GS), and with NO which is bound sideways (η2-MS2). In [Ru(CN)5NO]2− and [Fe(CN)5NO]2− ions, the MS2 state lies 1.1–1.4 eV above the GS state and 0.3–0.6 eV below the MS1 state, but in the [Ru(NH3)5NO]3+ ion, the MS2 state is slightly above the MS1. In the visible region, the electronic spectrum of ruthenium nitrosyl complexes contains metal-to-ligand charge transfer bands, 4dπ(Ru)e(π* NO). Using time-dependent density functional theory calculations it is possible to explain why the MS2 state of [Ru(NH3)5NO]3+ has not been observed experimentally. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 636–645, 2000