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

The properties of the [Ru(NH3)(5)NO](3+) and [Ru(CN)(5)NO](2-) ions are inv estigated by density functional theory and compared with those of [Fe(CN)(5 )NO](2-). DFT calculations show that the electronic ground-state potential surface of these nitrosyl complexes has local minima (metastable states) wi th oxygen-bonded NO (MS1), i.e., inverted from the usual N-bonded species ( GS), and with NO which is bound sideways (eta (2)-MS2). In [Ru(CN)(5)NO](2- ) and [Fe(CN)(5)NO](2-) ions, the MS2 state lies 1.1-1.4 eV above the GS st ate and 0.3-0.6 eV below the MS1 state, but in the [Ru(NH3)(5)NO](3+) ion, the MS2 state is slightly above the MS1. Ln the visible region, the electro nic spectrum of ruthenium nitrosyl complexes contains metal-to-ligand charg e transfer bands, 4d(pi) (Ru) --> e(pi* NO). Using time-dependent density f unctional theory calculations it is possible to explain why the MS2 state o f [Ru(NH3)(5)NO](3+) has not been observed experimentally. (C) 2000 John Wi ley & Sons, Inc.