SYNTHESIS AND CRYSTAL-STRUCTURE OF NICKEL(II) COMPLEXES OF MACROBICYCLIC LIGANDS - IDENTIFICATION AND ELECTRON-TRANSFER REACTIONS OF THE CORRESPONDING NICKEL(III) COMPLEXES IN SOLUTION

The macrobicyclic complex [NiL1(ClO4)]ClO4 (L1 = 1 5-oxa-1,5,8,12-tetr aazabicyclo[10.5.2]nonadecane) and the monocyclic precursor [NiL2(NCMe )][ClO4]2, [L2 = ,N'-bis(3-aminopropyl)-1-oxa-4,7-diazacyclononane] ha ve been prepared and their crystal structures determined: [NiL1(ClO4)] ClO4, space group P2(1)/n, a = 13.580(6), b = 15.400(8), c = 10.418(4) angstrom, beta = 97.91(2)degrees, Z = 4, R = 0.067, R' = 0.069; [NiL2 (NCMe)][ClO4]2, monoclinic, space group Cc, a = 9.182(1), b = 19.859(3 ), c-12.903(2) angstrom, beta = 100.99(1)degrees, Z = 4, R = 0.063, R' = 0.065. In each of these species the complexed cation is six-co-ordi nate with the ether oxygen co-ordinated 'axially' at distances of 2.10 9(6) and 2.189(12) angstrom, respectively. However, the equatorial co- ordination is significantly different. In [NiL1-(ClO4)]+ the nickel at om is coplanar with the four nitrogen donors of the 14-membered macroc yclic ring. In [NiL2(NCMe)]2+ one pendant arm is axial (trans to the e ther oxygen) with an acetonitrile molecule in the equatorial plane. Co planarity of the equatorial donor set is not realized in this cation. The sixth position in [NiL1(ClO4)]+ is occupied by a weakly bound perc hlorate ion [Ni-O 2.373(7) angstrom]. The corresponding nickel(III) co mplexes may be generated by Co3+(aq) oxidation in aqueous media or NO in non-aqueous media. Electron spin resonance measurements are consis tent with an octahedral d7 ion with the spectra obtained being sensiti ve to the nature of the nuclei in the sixth site. The kinetics of redu ction of the nickel(III) macrobicyclic ligand complex and its thiatetr aaza and pentaaza analogues with two outer-sphere electron-transfer re agents has been studied. Rapid electron self-exchange rate constants h ave been evaluated for both the aqua and chloro species [NiL(X)]n+ (X = H2O, n = 3; X = Cl, n = 2), with a sensitivity to the nature of the axial ligands being observed.