XRD and EXAFS studies of azomethynic copper metallochelates as models of blue copper proteins

The structure of two biomimetic copper complexes bis[4-benzylaldimino-3-methyl-l-phenyl-5-thio (seleno)pyrazolato]copper(II)-(36) 32N6X2Cu (where X = S, Se) have been studied and X-ray patterns of these compounds have been prepared using the Rietveld refinement technique. Both complexes crystallized in a monoclinic lattice, space group-C2/c(15). The unit-cell parameters are a = 28.917(3) angstrom; b = 7.000(2) angstrom; c = 17.550(4) angstrom; beta= 106.869(l) (1) for C36H32CuN6S2 and a = 29.126(6) angstrom; b 7.042(4) angstrom; c = 17.228(2) angstrom; beta= 105.587(2) for C36H32CuN6Se2. Analysis of the copper and selenium K-edge X-ray absorption spectra (EXAFS) of these complexes show that a copper atom is in pseudo-tetrahedric ligand environment N2X2 with typical Cu-N bonds (R=2.00-2.01 angstrom) and significantly different Cu-S and Cu-Se bonds (R=2.27 angstrom and R = 2.41 angstrom, respectively) because of different sulfur and selenium ion radii. 0 2004 International Centre for Diffraction Data.