SYNTHESIS, CHARACTERIZATION AND STRUCTURE OF THE HIGHLY STERICALLY CONGESTED COMPLEX (3,14-DIMETHYL-14-NITROMETHYL-2,6,13,17-TETRAAZATRICYCLO[16.4.0.0(7.12)]DOCOS-2-ENE)-NICKEL DIPERCHLORATE AND STRUCTURE OF

Abstract

The reaction of the diimine complex [NiL1][ClO4]2 (L1 = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0(7.12]docosa-2,13-diene), containing cyclohexane subunits fused to the five-membered chelate rings, with nitromethane in the presence of triethylamine produced the highly sterically congested complex [NiL2][ClO4]2 (L2=3,14-dimethyl-14-nitromethyl-2,6,13,17-tetraazatricyclo[16.4.0.0(7.12]docos-2-ene) containing one nitromethyl pendant arm. The electronic spectrum of [NiL2]2+ in nitromethane solution shows the d-d band at ca. 490 nm (epsilon = 170 dm3 mol-1 cm-1). The wavelength and the molar absorption coefficient are extraordinarily longer and larger, respectively, than those for square-planar nickel(II) complexes of L1 and other related 14-membered polyaza macrocycles. The crystal structures of [NiL1][ClO4]2 and, [NiL2][ClO4]2 revealed that the former has normal square-planar geometry with the nickel atom lying on the N4 plane, whereas the latter has a severely distorted square-planar geometry with the metal atom 0.118 angstrom out of the mean plane of the donor nitrogen atoms. The steric effects of the substituents of the complexes on the geometry and the spectra are discussed. Crystal data: for [NiL1][ClO4]2, monoclinic, space group P2(1)/n, a = 10.423(3), b = 8.9375(6), c = 13.457(3) angstrom, beta = 94.459(12)-degrees, Z = 2, R = 0.056 and R' = 0.057 for 2349 independent reflections with F(o)2 > 3sigma(F(o)2); for [NiL1] [ClO4]2, monoclinic, space group P2(1)/n, a = 11.968(3), b = 12.6208(14), c = 19.358(6) angstrom, beta = 105.008(15)-degrees, Z = 4, R = 0.046 and R' = 0.045 for 3382 independent reflections with F(o)2 > 3sigma(F(o)2).