EPR insensitivity of the metal-nitrosyl spin-bearing moiety in complexes [LnRuII-NO.]k

A survey of 18 paramagnetic species [LnRu(NO)](k), including seven new examples studied by in situ electrolysis, reveals a surprisingly narrow range of EPR parameters despite a wide variety of ligands such as pyridine, polypyridines, imines, amines, nitriles, phosphanes, carbonyl, cyclopentadienides, halides, hydride, hydroxide, thiocyanate or cyanide: g(1) = 2.015 +/- 0.02, g(2) = 1.990 +/- 0.015, g(3) = 1.892 +/- 0.03, g(av) = 1.968 +/- 0.02, Deltag = g(1) - g(3) = 0.122 +/- 0.037, A(2)(N-14) = 3.3 +/- 0.5 mT. This rather small variability, smaller still if the organometallic compounds are excluded, differs from the wider range of EPR data reported for nitrosyliron species with S = 1/2; apparently, the {RuNO}(7) configuration involves a rather invariant and relatively covalent metal-NO interaction. DFT calculations were employed for [(NC)(5)Ru(NO)](3-) to reproduce the EPR data, to evaluate the spin distribution (58% spin density on NO), and to reveal structural changes on reduction such as the Ru-N-O bending and Ru-NO bond lengthening. In addition, the possibility of staggered and eclipsed conformations is discussed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.