A pentaammineruthenium(III) dimer with the novel bridging ligand 4,4′-dicyanamidobiphenyl dianion

Article abstract of DOI:10.1139/v96-247

The novel ligand 4,4′-dicyanamidobiphenyl dianion (bp^2-) has been synthesized and characterized by ¹³C NMR spectroscopy, cyclic voltammetry, and crystallography. The crystal structure of [Ph₄As]₂[bp]·H₂O showed that bp^2- is approximately planar with a dihedral angle of 8.2° between phenyl ring planes and the cyanamide groups in an ami conformation. The water of crystallization is asymmetrically hydrogen bonded between cyanamide groups of adjacent bp^2- ions. The crystal data for C₆₂H₄₈N₄As₂+H₂O are monoclinic crystal system and space group P2₁/c with a = 12.998(5) A?, b = 13.465(4) A?, c = 28.703(13) A?, β = 98.94(3)°, V = 4963(3) A?³, and Z = 4. The structure was refined by using 4555 reflections with I > 2.5σ(I) to an R factor of 0.058. The complex, [{(NH₃}₅Ru}₂(μ-bp)][X]₄, where X = tosylate or PF₆^- ions, was also synthesized and characterized by ¹H NMR spectroscopy, cyclic voltammetry, spectroelectrochemistry, and temperature-dependent magnetic susceptibility measurements. From cyclic voltammetry measurements, the comproportionation constants to form the mixed-valence complex [{(NH₃}₅Ru)₂(μ-bp)]³⁺ were estimated to be 4.1, 16, and 22 in water, acetonitrile, and nitromethane, respectively. The trend and magnitude of K_c suggests solvent valence trapping of a weakly coupled Class II ion. The MMCT band of the mixed-valence complex had to be deconvoluted from the low-energy LMCT band and had the following properties in acetonitrile, ν_max = 8400 cm^-1, εmax = 3300 M^-1 cm^-1, and Δν_1/2 = 3300 cm^-1. The weak superexchange mediating properties of bp^2- compared to 1,4-dicyanamidobenzene dianion were suggested to arise from the larger barrier to the formation of the radical anion bp^-.

Full text of DOI:10.1139/v96-247

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.