Establishing the NO oxidation state in complexes [Cl(5)(NO)M](n-), M = Ru or Ir, through experiments and DFT calculations

Predominantly NO-centered reduction was observed by EPR and IR spectroelectrochemistry to occur reversibly at low temperatures for [Cl(5)Ir(NO)](-). In contrast, the [Cl(5)Ru(NO)](2-) ion was found to undergo only irreversible reduction but reversible oxidation to a ruthenium(III) species at -40 degrees C. DFT calculations were used to establish the electronic structures and to rationalise the different stabilities. The calculations also reveal orientation-dependent energies and EPR properties between staggered and eclipsed conformations.