title: Syntheses, structures, and properties of imidazolate-bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) dinuclear complexes of a single macrocyclic ligand with two hydroxyethyl pendants.
abstract: The imidazolate-bridged homodinuclear Cu(II)-Cu(II) complex, [(CuimCu)L]ClO(4).0.5H(2)O (1), and heterodinuclear Cu(II)-Zn(II) complex, [(CuimZnL(-)(2H))(CuimZnL(-)(H))](ClO(4))(3) (2), of a single macrocyclic ligand with two hydroxyethyl pendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,2(11,14)]triaconta-1,11,13,24,27,29-hexaene), have been synthesized as possible models for copper-zinc superoxide dismutase (Cu(2),Zn(2)-SOD). Their crystal structures analyzed by X-ray diffraction methods have shown that the structures of the two complexes are markedly different. Complex 1 crystallizes in the orthorhombic system, containing an imidazolate-bridged dicopper(II) [Cu-im-Cu](3+) core, in which the two copper(II) ions are pentacoordinated by virtue of an N4O environment with a Cu.Cu distance of 5.999(2) A, adopting the geometry of distorted trigonal bipyramid and tetragonal pyramid, respectively. Complex 2 crystallizes in the triclinic system, containing two similar Cu-im-Zn cores in the asymmetric unit, in which both the Cu(II) and Zn(II) ions are pentacoordinated in a distorted trigonal bipyramid geometry, with the Cu.Zn distance of 5.950(1)/5.939(1) A, respectively. Interestingly, the macrocyclic ligand with two arms possesses a chairlike (anti) conformation in complex 1, but a boatlike (syn) conformation in complex 2. Magnetic measurements and ESR spectroscopy of complex 1 have revealed the presence of an antiferromagnetic exchange interaction between the two Cu(II) ions. The ESR spectrum of the Cu(II)-Zn(II) heterodinuclear complex 2 displayed a typical signal for mononuclear trigonal bipyramidal Cu(II) complexes. From pH-dependent ESR and electronic spectroscopic studies, the imidazolate bridges in the two complexes have been found to be stable over broad pH ranges. The cyclic voltammograms of the two complexes have been investigated. Both of the two complexes can catalyze the dismutation of superoxide and show rather high activity.
authors.affiliation: State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210093, P. R. China. chem1121@nju.edu.cn
authors.forename: Dongfeng
authors.initials: D
authors.lastname: Li
authors.forename: Shuan
authors.initials: S
authors.lastname: Li
authors.forename: Dexi
authors.initials: D
authors.lastname: Yang
authors.forename: Jiuhong
authors.initials: J
authors.lastname: Yu
authors.forename: Jin
authors.initials: J
authors.lastname: Huang
authors.forename: Yizhi
authors.initials: Y
authors.lastname: Li
authors.forename: Wenxia
authors.initials: W
authors.lastname: Tang
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006575:Heterocyclic Compounds, 3-Ring / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry*; D007202:Indicators and Reagents; D008024:Ligands; D008280:Magnetics; D008958:Models, Molecular; D008968:Molecular Conformation; D013056:Spectrophotometry, Ultraviolet; D013482:Superoxide Dismutase / Q000378:metabolism; D015032:Zinc / Q000737:chemistry*
chemical_list: C482498:3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo(22,2,2,2(11,14))triaconta-1,11,13,24,27,29-hexaene; D006575:Heterocyclic Compounds, 3-Ring; D007093:Imidazoles; D007202:Indicators and Reagents; D008024:Ligands; D003300:Copper; D013482:Superoxide Dismutase; D015032:Zinc