Magnetic and structural studies of novel tetranickel hydroxamates

摘要

The dinickel(II) compound [Ni-2(mu-OAc)(2)(OAc)(2)(mu-H2O)(asy dmen)(2)]center dot 2.5H(2)O, 1; undergoes facile reaction in a [Ni-4(mu-OAc)(3)(mu-BA)(3)(asy.dmen)(3)][OTf](2)center dot H2O, 2, in which the bridging acetates, bridging two nickel atoms in 1, undergo a carboxylate shift from the mu(2)-eta(1):eta(1) bridging mode of binding to the mu(3)-g(1):g(2) bridging three nickel atoms in the tetramer. The structure of complex 2 was determined by single-crystal X-ray crystallography. The two monodentate acetates, water and two bidentate bridging acetates of two moles of complex 1 are replaced by three monodentate bridging acetates and three benzohydroxamates. Three nickel atoms in the tetramer, Ni(2), Ni(3) and Ni(4) are in a N2O4 octahedral environment, while the fourth nickel atom Ni(1) is in an O(6) octahedral environment. The Ni-Ni separations are Ni(1)-Ni(2) = 3.108 angstrom, Ni(1)-Ni(3) = 3.104 angstrom and Ni(1)-Ni(4) = 3.110 angstrom, which are longer than previously studied in dinuclear urease inhibited models but shorter than in the nickel(II) tetrameric glutarohydroxamate complex [Ni-4(mu-OAc)(2)(mu-gluA(2))(2)(tmen)(4)][OTf](2), isolated and characterized previously in this laboratory. Magnetic studies of the tetrameric complex show that the four Ni(II) ions are ferromagnetically coupled, leading to a total ground spin state S-T = 4. Three analogous tetranuclear nickel hydroxamates were prepared from AHA and BHA and the appropriate dinuclear complex with either sy.dmen or asy.dmen as capping ligands. ratio with benzohydroxamic acid (BHA) in ethanol to give the novel nickel(II) tetranuclear hydroxamate complex