STRUCTURAL AND FUNCTIONAL MODELS FOR THE DINUCLEAR COPPER ACTIVE-SITEIN CATECHOL OXIDASES - SYNTHESES, X-RAY CRYSTAL-STRUCTURES, MAGNETIC AND SPECTRAL PROPERTIES, AND X-RAY-ABSORPTION SPECTROSCOPIC STUDIES INSOLID-STATE AND IN SOLUTION

Two novel tridentate dinucleating ligands containing benzimidazole wer e prepared, 1,3-bis(2-benzimidazolyl)-2-propanol (Hbbp, 1) and 1,5-bis (2-benzimidazolyl)-3-pentanol (Hbbpen, 2). Their complexing properties toward copper were studied in order to obtain structural and function al models for catechol oxidases. Syntheses and crystal structures of d inuclear Cu(II) complexes derived from these ligands are reported. [Cu (2)bbp(2)](ClO4)(2) . 2MeOH, 3, crystallizes in the triclinic space gr oup <P(1)over bar> with the following unit cell parameters: a = 7.702( 3) Angstrom, b = 10.973(6) Angstrom, c = 12.396(6) Angstrom, alpha = 1 00.59(4)degrees, beta = 99.02(4)degrees, gamma = 98.90(4)degrees, V = 998.7(8) Angstrom(3), and Z = 1. [Cu(2)bbpen(2)](ClO4)2 . 3MeOH, 4, cr ystallizes in the orthorhombic space group Peen, with the following un it cell parameters: a = 17.478(9) Angstrom, b = 18.795(8) Angstrom, c = 13.888(6) Angstrom, V = 4562.2(4) Angstrom(3), and Z = 4. Magnetic s usceptibility measurements in the temperature ranges 4.6-459 K (3) and 4.6-425 K (4) indicate an antiferromagnetic coupling between the Cu(I I) centers of both complexes. In order to determine the structures of the complexes in solution, XAS spectra (EXAFS and XANES) were recorded in the solid state and in solution. The interpretation of these data, including multiple scattering calculations, together with UV-vis titr ations, shows that the complexes have the same structure in the crysta lline state as well as in methanolic solution. Complex 4 is able to ox idize 3,5-di-tert-butylcatechol (3,5-DTBC) to the quinone (catecholase activity). This reaction was also studied by XAS and UV-vis spectrosc opy. These measurements reveal the reduction of Cu(II) to Cu(I) accomp anied by a decrease of the coordination number.