The Redox Series M(bpy)2(Q)n+, M = Ru or Os, Q = 3,5-Di-tert-butyl-N-phenyl-1,2-benzoquinonemonoimine. Isolation and a Complete X and W Band EPR Study of the Semiquinone States (n = 1)

, , , , and . Inorganic Chemistry 44 (8): 2843--2847 (2005)


M(bpy)2(Q)(PF6) (bpy = 2,2'-bipyridyl; M = Ru, Os; Q = 3,5-di-tert-butyl-N-phenyl-1,2-benzoquinonemonoimine) were isolated and studied by X and W band EPR in a CH2Cl2 soln. at ambient temps. and at 4 K. For M = Ru, the 14N hyperfine splitting confirms the RuII/semiquinone formulation, although at a \textgreater 1 mT, the 99,101Ru satellite coupling is unusually high. W band EPR allowed the authors to det. the relatively small g anisotropy Dg = g1 - g3 = 0.0665 for the Ru complex. The Os analog exhibits a much higher difference Dg = 0.370, which is attributed not only to the larger spin-orbit coupling const. of Os vs. that of Ru but also to a higher extent of metal contribution to the singly occupied MO. The difference DE between the oxidn. and redn. potentials of the radical complexes is larger for the Ru compd. (DE = 0.87 V) than for the Os analog (DE = 0.72), confirming the difference in metal/ligand interaction. The electrochem. generated states M(bpy)2(Q)n+, n = 0, 1, 2, and 3, were also characterized using UV-visible-near-IR spectroelectrochem. on SciFinder(R)

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