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Magnetic and structural studies of novel tetranickel hydroxamates |
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| Authors: | Ahmed Z Eltayeb David A Brown Christopher E Anson |
| Institution: | a Department of Chemistry, Faculty of Science, University of Khartoum, Khartoum, Sudan b Centre for Synthesis and Chemical Biology, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland c Institut für Anorganische Chemie, Karlsruhe Institute of Technology, Universität Karlsruhe, Engesserstr. 15, D-76128 Karlsruhe, Germany |
| Abstract: | 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. |
| Keywords: | OAc CH3COO&minus Opiv (CH3)3CCOO&minus OAcF CF3COO&minus tmen N N N1 N1-tetramethylethylenediamine sy· dmen N N1-dimethylethylenediamine asy· dmen N N-dimethylethylenediamine Im imidazole BHA benzohydroxamic acid BA benzohydroxamate anion AHA acetohydroxamic acid AA acetohydroxamate anion gluH2A2 glutarodihydroxamic acid gluA2 glutarodihyroxamate dianion |
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