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-).
abstract: The new redox systems [(acac)2 Ru(mu-Q1)Ru(acac)2](n) (1(n)) and [(acac)2 Ru(mu-Q2)Ru(acac)2](n) (2(n)) with Q1 = 1,10-phenanthroline-5,6-dione and Q2 = 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-Q1)*- Ru(III) species with partially coupled semiquinone and ruthenium(III) centers. In contrast, a Ru(III)(mu-Q2)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-Q1)2- Ru(III) for 1(-) with a Ru(III)-typical EPR response and as Ru(II)(mu-Q2)*- 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)0Ru(III), Ru(III)(mu-Q)2- Ru(IV) or Ru(III)(mu-Q)*- Ru(III), the last description is favored. The reasons for identical or different oxidation state combinations are discussed.
authors.affiliation: Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai, 400076, India.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Ghumaan
authors.forename: Biprajit
authors.initials: B
authors.lastname: Sarkar
authors.forename: Srikanta
authors.initials: S
authors.lastname: Patra
authors.forename: Joris
authors.initials: J
authors.lastname: van Slageren
authors.forename: Jan
authors.initials: J
authors.lastname: Fiedler
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri