| Abstract
| - Two imidazolate-bridged bimetallic complexes, [(CuimCu)L]ClO4·0.5H2O (1) and [(CuimZnL-2H)(CuimZnL-H)](ClO4)3 (2), of a single macrocyclic ligand with two hydroxyethyl pendants (L) have been obtained as models of copper−zinc superoxide dismutase. The X-ray crystal structures, magnetic, ESR, and electronic spectroscopic properties, and electrochemistry of the two imidazolate-bridged complexes are reported.
- The imidazolate-bridged homodinuclear Cu(II)−Cu(II) complex, [(CuimCu)L]ClO4·0.5H2O (1), and heterodinuclearCu(II)−Zn(II) complex, [(CuimZnL-2H)(CuimZnL-H)](ClO4)3 (2), of a single macrocyclic ligand with two hydroxyethylpendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,211,14]triaconta-1,11,13,24,27,29-hexaene), have been synthesized as possible models for copper−zinc superoxide dismutase (Cu2,Zn2-SOD). Theircrystal structures analyzed by X-ray diffraction methods have shown that the structures of the two complexes aremarkedly 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 witha Cu···Cu distance of 5.999(2) Å, 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 asymmetricunit, in which both the Cu(II) and Zn(II) ions are pentacoordinated in a distorted trigonal bipyramid geometry, withthe Cu···Zn distance of 5.950(1)/5.939(1) Å, respectively. Interestingly, the macrocyclic ligand with two arms possessesa chairlike (anti) conformation in complex 1, but a boatlike (syn) conformation in complex 2. Magnetic measurementsand ESR spectroscopy of complex 1 have revealed the presence of an antiferromagnetic exchange interactionbetween the two Cu(II) ions. The ESR spectrum of the Cu(II)−Zn(II) heterodinuclear complex 2 displayed a typicalsignal for mononuclear trigonal bipyramidal Cu(II) complexes. From pH-dependent ESR and electronic spectroscopicstudies, the imidazolate bridges in the two complexes have been found to be stable over broad pH ranges. Thecyclic voltammograms of the two complexes have been investigated. Both of the two complexes can catalyze thedismutation of superoxide and show rather high activity.
|
