SYNTHESIS, PROPERTIES, AND X-RAY STRUCTURES OF NICKEL(I) COMPLEXES OF POLYAZA MACROTRICYCLIC LIGANDS

Square-planar Ni(I) complexes of various saturated polyaza macrotricyclic ligands 1-7 have been prepared by the reduction of Ni(II) complexes with Na(Hg) in MeCN solutions, and some Ni(I) complexes [Ni(L)]ClO4 (L = 1-5) were isolated as crystals. UV/vis spectra of the Ni(I) complexes show a d-d transition band at 538-600 nm, which is at ca. 100 nm longer wavelength than those of Ni(II) complexes, with relatively large extinction coefficients (epsilon = 250-1000). EPR spectra of the Ni(I) complexes show anisotropic axial g(parallel-to) and g(perpendicular-to) (g(parallel-to) > g(perpendicular-to)) values or rhombic g1, g2, and g3 values. [Ni(1)]ClO4.CH3CN (1 = C12H27N7) crystallizes in the triclinic space group P1BAR with a = 9.407 (1) angstrom, b = 9.577 (2) angstrom, c = 13.216 (4) angstrom, alpha = 69.20 (2)-degrees, beta = 78.68 (2)-degrees, gamma = 61.81 (2)-degrees, and Z = 2. The structure was solved by the heavy-atom method and refined anisotropically to R values of R = 0.049 and R(w) = 0.052 for 2659 observed reflections (F greater-than-or-equal-to 3-sigma(F)) measured with Mo K-alpha radiation on a CAD-4 diffractometer. [Ni(3)]ClO4 (3 = C12H26N6) crystallizes in the orthorhombic space group Pna2(1) with a = 16.239 (1) angstrom, b = 7.7723 (1) angstrom, c = 13.460 (2) angstrom, and Z = 4. The structure was solved by the heavy-atom method and refined anisotropically to R values of R = 0.053 and R(w) = 0.057 for 1053 observed reflections measured with Mo K-alpha radiation on a CAD-4 diffractometer. The X-ray crystal structures of [Ni(1)]ClO4.CH3CN and [Ni(3)]ClO4 indicate that the compounds have square-planar geometry. [Ni(1)]ClO4.CH3CN shows a square-pyramidal distortion and [Ni(3)]ClO4 shows a tetrahedral distortion of the donor nitrogen atoms. The two 1,3-diazacyclopentane ring moieties in [Ni(3)]ClO4 are located anti and almost perpendicular to the plane of the 14-membered macrocycle. The Ni(I) complexes of 1 and 3 show two sets of Ni-N bond distances, each set consisting of two cis-positioned Ni-N bonds involving a six-membered chelate ring, rather than a simple expansion of macrocyclic hole, average 1.893 (2) and 1.936 (2) A for [Ni(1)]ClO4.CH3CN and average 1.859 (7) and 1.974 (7) angstrom for [Ni(3)]ClO4.