Magnetic and structural studies of novel tetranickel hydroxamates

The dinickel(II) compound [Ni2(μ-OAc)2(OAc)2(μ-H2O)(asy·dmen)2]·2.5H2O, 1; undergoes facile reaction in a 1:2 molar ratio with benzohydroxamic acid (BHA) in ethanol to give the novel nickel(II) tetranuclear hydroxamate complex [Ni4(μ-OAc)3(μ-BA)3(asy·dmen)3][OTf]2·H2O, 2, in which the bridging acetates, bridging two nickel atoms in 1, undergo a carboxylate shift from the μ2-η1:η1 bridging mode of binding to the μ3-η1:η2 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 Å, Ni(1)–Ni(3) = 3.104 Å and Ni(1)–Ni(4) = 3.110 Å, which are longer than previously studied in dinuclear urease inhibited models but shorter than in the nickel(II) tetrameric glutarohydroxamate complex [Ni4(μ-OAc)2(μ-gluA2)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 ST = 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.

The reaction of the urease model complex 1, [Ni2(μ-OAc)2(OAc)2(μ-H2O)(asy·dmen)2]·2.5H2O, with benzohydroxamic acid (BHA) gives the novel nickel(II) tetranuclear hydroxamate complex [Ni4(μ-OAc)3(μ-BA)3(asy·dmen)3][OTf·H2O], 2, in which the bridging acetates undergo a carboxylate shift. Magnetic studies of the tetrameric complex show that the four Ni(II) ions are ferromagnetically coupled, leading to a total ground spin state ST = 4.Figure optionsDownload as PowerPoint slide