THE SYNTHESIS, STRUCTURE AND SOD-LIKE BEHAVIORS OF A MU-IMIDAZOLATO-DICOPPER(II) COMPLEX WITH A BINUCLEATING HEXAAZAMACROCYCLE

The synthesis, crystal structure and magnetic properties of the imidaz olate-bridged dinuclear copper(II) complex [LCu2(Im)(DMSO)(2)](ClO4)(3 )(DMSO), where ImH is imidazole, and L is 3, 6, 9, 17, 20, 3-hexaazatr icyclo[23.3.1.1(11,13)]triaconta-1(29), 11(30), 12, 14, 25(26), 27-hex aene, have been studied. Single crystal X-ray diffraction determinatio n reveals the distorted tetragonal pyramid geometries of the imidazola te bridged dicopper(II) center are incorporated within the binucleatin g macrocycle. Both copper atoms are five-coordinated by four basal nit rogen atoms (three from the macrocycle and one from the imidazolate) a nd one oxygen atom from the DMSO molecule. Two coordinated DMSO molecu les are situated at the same side of the macrocycle. The Cu-Cu separat ion in the complex is 5.93 Angstrom. Magnetic measurements and ESR spe ctroscopy studies exibit an antiferromagnetic exchange interaction wit h a coupling constant of J = - 26.94 cm(-1). Investigations on the pH- dependent ESR of the title compound in frozen 50% aqueous DMSO solutio n confirm the existence of the bridged cation [LCu2(Im)](3+) as a majo r species in solution mainly in the range 5.2 less than or equal to pH less than or equal to 11.5. The imidazolate bridge is broken in the p H range of 5.2-3.3, which is close to that for the native enzyme. (C) 1998 Elsevier Science Inc. All rights reserved.