SYNTHESIS, CRYSTAL-STRUCTURE, AND PROPERTIES OF A NEW IMIDAZOLATE-BRIDGED COPPER-ZINC HETEROBINUCLEAR COMPLEX WITH TRIETHYLENETETRAMINE LIGANDS

The syntheses of the mononuclear [(trien)Cu(imH)](ClO4)(2) and binuclear [(trien)Cu(im)Cu(trien)](ClO4)(3) . H2O and [(trien)Cu(im)Zn(trien)](ClO4)(3) . H2O complexes, where trien = triethylenetetramine and im is the imidazolate ion, are described. Single-crystal X-ray diffraction studies of the heterobinuclear complex reveals the geometry of the imidazolate-bridged Cu(II)-Zn(II) center. The copper or zinc atom is pentacoordinate, with four trien nitrogen atoms forming an approximate plane and a bridging imidazolate in the apical position of a distorted tetragonal pyramid. The Cu-Zn distance is 6.081(2) Angstrom. pH-dependent ESR studies of frozen 50% aqueous DMSO solutions of [Cu(trien)](ClO4)(2), [Cu(trien)(imH)](ClO4)(2), and [(trien)Cu(im)Zn(trien)](ClO4)(3) . H2O complexes have also been carried out and show that the bridged cation [(trien)Cu(im)Zn(trien)](3+) exists as a major species in solution over the range 10.3 less than or equal to pH less than or equal to 12.4. As the pH is lowered to 9.6-10.3, the bridge is broken on the copper side, which is different from case of [(dtma)Cu(im)Zn(dtma)]ClO4 and [(tren)Cu(im)Zn(tren)][ClO4)(3), where the bridge is broken on the zinc side.