SYNTHESIS, SPECTROSCOPIC AND STRUCTURAL CHARACTERIZATION OF BIS(ACETATO)TETRAKIS(IMIDAZOLE)COPPER(II) - A MODEL COMPLEX FOR DNA-BINDING

The complex bis(acetato)tetrakis(imidazole)copper(II), [Cu(Im)4(OAc)2] (2), has been prepared by the reaction of excess imidazole with Cu2(OAc)4. Complex 2 exhibits a magnetic moment of 1.88 BM, consistent with one unpaired electron and the formulation of the complex as a Cu(II) monomer. The frozen-solution ESR spectrum exhibits axial symmetry with g(parallel-to) and g(perpendicular-to) values of 2.221 and 2.040, respectively, and A(parallel-to)(Cu) = 181 x 10(-4) cm-1. The g(perpendicular-to) signal and lowest-field component of the g(parallel-to) signal exhibit N-14 super-hyperfine structure that consists of nine lines with A(perpendicular-to) (N) = 15 x 10(-4) and A(parallel-to) (N) = 10 x 10(-4) cm-1. The ESR data are consistent with the tetragonally elongated chromophore CuN4...O2. Complex 2 crystallizes in the space group C2/c with a = 13.187(2), b = 8.591(1), c = 17.644(2) angstrom, beta = 104.13(1), V = 1938.4(5) angstrom3, Z = 4, D(calc) = 1.556 g/cm3. The relevance of complex 2 to DNA binding of copper(II) imidazole complexes is discussed.