PHOTOCHEMICAL ACTIVATION OF CARBON-DIOXIDE BY VISIBLE-LIGHT MEDIATED BY COBALT(II) AND NICKEL(II) COMPLEXES OF 1,6-BIS(BENZIMIDAZOL-2-YL)-2,5-DITHIAHEXANE (BBDH)

Reactions between crystalline Ni(NO3)(2) or Co(ClO4)(2) 6H(2)O and 1,6 -bis(benzimidazol-2-yl)-2,5-dithiahexane (BBDH) in ethanol afford the insolubles [Ni(BBDH)(H2O)(2)](NO3)(2) or [Co(BBDH)(H2O)(2)](ClO4)(2) a nd coloured solutions. The action of CO2 and visible light on these su spensions at room temperature yields new nickel(II) or cobalt(II) 2- c arboxylato benzimidazolates, [O2C-BzIm](2-), of formula [Ni-2(BBDH)(2) (mu(2)-O2C-BzIm)](NO3)(2) (I) and [Co-2(BBDH)(2)(mu(2)-O2C-BzIm)] (ClO 4)(2) (II), respectively. The crystal and molecular structure of I and II have been elucidated by single crystal X-ray analysis. The complex I crystallizes in the monoclinic space group C2/c, with a = 15.371(3) , b = 13.393(3), c = 22.790 (4) Angstrom, and beta = 99.54(4)degrees. The unit cell comprises four formula units with half the binuclear cat ion complex in the asymmetric unit. The [O2C-BzIm](2-) bridges two dis torted octahedral nickel(II) ions having a Ni-Ni distance of 5.397(2) Angstrom. Complex II crystallizes in the triclinic space group P1, wit h cell data a = 13.351(5), b = 18.960(5), c = 11.379(3) Angstrom, alph a = 91.14(2), beta = 107.93(3), and gamma = 100.88(3)degrees. The cati on complex consist of a dimeric unit with two distorted octahedral cob alt(II) ions being bridged by a 2-carboxylatobenzimidazolato anion wit h a Co-Co distance of 5.285(6) Angstrom. IR spectra are reported. A pl ausible mechanism by which complexes I and II are formed is also repor ted.