A New Coordination Mode of the Photometric Reagent Glyoxalbis(2-hydroxyanil) (H2gbha): Bis-Bidentate Bridging by gbha2- in the Redox Series (μ-gbha)Ru(acac)22n (n = -2, -1, 0, +1, +2), Including a Radical-Bridged Diruthenium(III) and a RuIII/RuIV Intermediate
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Inorganic Chemistry 44 (24): 8715--8722 (2005)

The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was obsd. for the 1st time in the complex (m-gbha)RuIII(acac)22 (1). D. functional theory calcns. of 1 yield a triplet ground state with a large (DE \textgreater 6000 cm-1) singlet-triplet gap. Intermol. antiferromagnetic coupling was obsd. (J $\approx$ -5.3 cm-1) for the solid. Complex 1 undergoes two 1-electron redn. and two 1-electron oxidn. steps; the five redox forms (μ-gbha)Ru(acac)22n (n = -2, -1, 0, +1, +2) were characterized by UV-visible-NIR spectroelectrochem. (NIR = near IR). The paramagnetic intermediates were also studied by EPR spectroscopy. The monoanion with a comproportionation const. Kc of 2.7 $\times$ 108 does not exhibit an NIR band for a RuIII/RuII mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion contg. ligand gbha.bul.3-, which binds two ruthenium(III) centers. A RuIII-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is obsd. as a result of antiferromagnetic coupling between one RuIII and the ligand radical. The EPR-active monocation (Kc = 1.7 $\times$ 106) exhibits a broad (Dn1/2 = 2600 cm-1) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3·5)2 formulation (class III) with a tendency toward class II (borderline situation). on SciFinder(R)
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