title: Inner Coordination Sphere Control of Metal-Metal Superexchange in Ruthenium Dimers.
abstract: The dinuclear Ru(III) complexes trans-[{(NH(3))(4)Ru(py)}(2)(&mgr;-L)][PF(6)](4), where py represents pyridine and L represents 1,4-dicyanamidobenzene dianion (dicyd(2)(-)) derivatives dicyd(2)(-) (1), Me(2)dicyd(2)(-) (2), Cl(2)dicyd(2)(-) (3), and Cl(4)dicyd(2)(-) (4), have been prepared and characterized by electronic absorption spectroscopy and cyclic voltammetry. A crystal structure of the complex trans-[{(NH(3))(4)Ru(py)}(2)(&mgr;-dicyd)][PF(6)](4).(1)/(2)H(2)O showed the dicyd(2)(-) ligand to be approximately planar with the cyanamido groups in a syn configuration. Crystal structure data are space group P2(1), with a, b, and c = 7.826(3), 20.455(7), and 14.428(5) Å, respectively, beta = 95.76 (3) degrees, V = 2296.7(14) Å(3), and Z = 2. The structure was refined by using 3292 reflections with I > 2.5sigma(I) to an R factor of 0.069. Solid state magnetic susceptibility measurements of the Ru(III)-Ru(III) dimers showed diamagnetic behavior at room temperature, and this is suggested to be due to strong antiferromagnetic superexchange via the HOMO of the dicyd(2)(-) ligand. The bridging ligand dependence of metal-metal coupling in the Ru(III)-Ru(II) complexes of 1, 2, 3, and 4 in acetonitrile solution was demonstrated by the trend in comproportionation constants, 1.5 x 10(6), 5.7 x 10(6), 1.4 x 10(4), and 1.1 x 10(3), respectively. In addition, comparison to the analogous pentaammineruthenium dimers showed that the magnitude of metal-metal superexchange could be controlled by the nature of the spectator ligand. Spectroelectrochemical methods were used to acquire the absorption spectra of the mixed-valence complexes, and the intervalence band properties were modeled with PKS theory. Metal-metal coupling in the Ru(III)-Ru(II) complexes of 1, 2, 3, and 4 was analyzed by using Hush and CNS theories.
authors.affiliation: Ottawa-Carleton Chemistry Institute, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6, Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1, Department of Chemistry, University of Montreal, Montreal, Quebec, Canada H3C 3J7, and St. Petersburg University, Universitekaja nab. 7-9, St. Petersburg 199034, Russia.
authors.forename: Ali R.
authors.initials: AR
authors.lastname: Rezvani
authors.forename: Corinne
authors.initials: C
authors.lastname: Bensimon
authors.forename: Benoit
authors.initials: B
authors.lastname: Cromp
authors.forename: Christian
authors.initials: C
authors.lastname: Reber
authors.forename: J. E.
authors.initials: JE
authors.lastname: Greedan
authors.forename: Veniamin V.
authors.initials: VV
authors.lastname: Kondratiev
authors.forename: Robert J.
authors.initials: RJ
authors.lastname: Crutchley