A PENTAAMMINERUTHENIUM(III) DIMER WITH THE NOVEL BRIDGING LIGAND 4,4'-DICYANAMIDOBIPHENYL DIANION

The novel ligand 4,4'-dicyanamidobiphenyl dianion (bp(2-)) has been sy nthesized and characterized by C-13 NMR spectroscopy, cyclic voltammet ry, and crystallography. The crystal structure of [Ph(4)As](2)[bp]. H2 O showed that bp(2-) is approximately planar with a dihedral angle of 8.20 between phenyl ring planes and the cyanamide groups in an anti co nformation. The water of crystallization is asymmetrically hydrogen bo nded between cyanamide groups of adjacent bp(2-) ions. The crystal dat a for C62H48N4As2+H2O an monoclinic crystal system and space group P2( 1)/c with a = 12.998(5) Angstrom, b = 13.465(4) Angstrom, c = 28.703(1 3) Angstrom, beta = 98.94(3)degrees, V = 4963(3) Angstrom(3), and Z = 4. The structure was refined by using 4555 reflections with I> 2.5 sig ma(I) to an R factor of 0.058. The complex, [{(NH3}Ru-5}(2)(mu-bp)][X] (4), where X = tosylate or PF6- ions, was also synthesized and charact erized by H-1 NMR spectroscopy, cyclic voltammetry, spectroelectrochem istry, and temperature-dependent magnetic susceptibility measurements. From cyclic voltammetry measurements, the comproportionation constant s to form the mixed-valence complex [{(NH3}Ru-5}(2)(mu-bp)](3+) were e stimated to be 4.1, 16, and 22 in water, acetonitrile, and nitromethan e, respectively. The trend and magnitude of K-c suggests solvent valen ce trapping of a weakly coupled Class II ion. The MMCT band of the mix ed-valence complex had to be deconvoluted from the low-energy LMCT ban d and had the following properties in acetonitrile, v(max) = 8400 cm(- 1), epsilon(max) = 3300 M(-1) cm(-1), and Delta v(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 bar rier to the formation of the radical anion bp(-).