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|Title: ||Sensitive oxidation state ambivalence in unsymmetrical three-center (M/Q/M) systems [(acac)(2)Ru(mu-Q)Ru(acac)(2)](n), Q=1,10-phenanthroline-5,6-dione or 1,10-phenanthroline-5,6-diimine (n = +, 0, -, 2-)|
|Authors: ||GHUMAAN, S|
VAN SLAGEREN, J
|Keywords: ||transition-metal complexes|
|Issue Date: ||2005|
|Publisher: ||AMER CHEMICAL SOC|
|Citation: ||INORGANIC CHEMISTRY, 44(9), 3210-3214|
|Abstract: ||The new redox systems [(acac)(2)Ru(u-Q(1))Ru(acac)(2)](n) (1(n)) and [(acac)(2)Ru(mu-Q(2))Ru(acac)(2)](n) (2(n)) with Q(1) = 1,10-phenanthroline-5,6-dione and Q(2) = 1,10-phenanthroline-5,6-diimine were studied for n = +, 0, -, and 2- using UV-Vis-NIR spectroelectrochemistry, and, in part, EPR and susceptometry. The ligands can bind the first metal (left) through the phenanthroline nitrogen atoms and the second metal (right) at the o-quinonoid chelate site. The neutral compounds are already different: Compound 1 is formulated as a Ru-II(mu-Q(1))(center dot-) Ru-III species with partially coupled semiquinone and ruthenium(III) centers. In contrast, a Ru-III(mu-Q(2))(2-) Ru-III structure is assigned to 2, which shows a weak antiferromagnetic spin-spin interaction (J = -1.14 cm(-1)) and displays an intense half-field signal in the EPR spectrum. The one-electron reduced forms are also differently formulated as Ru-II(mu-Q(1))(2-) Ru-III for 1(-) with a Ru-III-typical EPR response and as Ru-II(mu-Q(2))(center dot-) Ru-II for 2- with a radical-type EPR signal at g = 2.0020. In contrast, both 1(2-) and 2(2-) can only be described as Ru-II(mu-Q)(2-) Ru-II species. The monooxidized forms 1(+) and 2(+) show very similar spectroscopy, including a Ru-III-type EPR signal. Although no unambiguous assignment was possible here for the alternatives Ru-II(mu-Q)Ru-0(III), Ru-III(mu-Q)(2-) Ru-IV or Ru-III(mu-Q)(center dot-) Ru-III, the last description is favored. The reasons for identical or different oxidation state combinations are discussed.|
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