Synthesis, characterization and activity of imidazolate-bridged and Schiff-base dinuclear complexes as models of Cu,Zn-SOD. A comparative study
Résumé
Two imidazolate-bridged diCu(II) and (CuZnII)-Zn-II complexes, [CuZn(dien)(2)(mu-Im)](ClO4)(3)center dot MeOH (1) and [Cu-2(dien)(2)(mu-Im)](ClO4)(3) (2) (Im = imidazole, dien = diethylenetriamine), and two complexes formed with Schiff base ligands, [CuZn(salpn)Cl-2] (3) and [Cu-2(salbutO)ClO4] (4) (H(2)salpn = 1,3-bis(salicylidenamino) propane, H(3)salbutO = 1,4-bis(salicylidenamino)butan-2-ol) have been prepared and characterized. The reaction of [Cu(dien)(ImH)](ClO4)(2) with [Zn(dien)(H2O)](ClO4)(2) at pH >= 11 yields complex 1; at lower pH, the Cu3Zn tetranuclear complex [(dien)Cu(mu-Im)(3)Zn(OH2)(ClO4)(2)](ClO4)(3) (1a) forms as the main reaction product. X-ray diffraction of 1a reveals that the complex contains a metal centered windmill-shaped cation having three blades with a central Zn ion and three peripheral capping Cu(dien) moieties bound to the central Zn ion through three imidazolate bridges. The four complexes are able to disproportionate 0(2)center dot(-) in aqueous medium at pH 7.8, with relative rates 4 > 1> 2 >> 3. [Cu-2(salbutO)](+) (4) is the most easily reducible of the four complexes and exhibits the highest activity among the SOD models reported so far; a fact related to the ligand flexibility to accommodate the copper ion in both Cu-I and Cu-II oxidation states and the lability of the fourth coordination position of copper facilitating stereochemical rearrangements.