An EXAFS investigation of the structures of bromocopper(II) complexes in some solutions

The structures of bromocopper(II) complexes in methanolic (M1, M2, M3, M4), ethanolic (E), and aqueous (H) solutions were determined by the analyses of the Cu K- and Br K-edge EXAFS spectra using a curve-fitting method. The molar concentrations of Cu and Br in these solutions prepared by CuBr2 and LiBr are 0.996 and 1.992 (M1), 1.015 and 5.381 (M2), 0.493 and 4.525 (M3), 0.260 and 4.073 (M4), 1.031 and 4.313 (E), and 0.982 and 5.426 (H). In M1 solution the interatomic distances for the Cu-Oeq, Breq-Cu, and Breq-Oeq (eq = equatorial) were 2.00A, 2.35A, and 3.15A respectively, and the Breq-Cu-Oeq angle was estimated as about 92 deg. Therefore, trans-dibromo bis(methanol)copper(II) complex with a slightly distorted planar structure was proposed to be dominant complex species in M1 solution. The interatomic distances in M2, M3, M4 and E solutions were 2.37A and 3.45A (average) for the Breq-Cu and Breq-Breq respectively. The Breq-Cu-Breq angle, paticularly in solutions M2 and E, was estimated as about 95 deg. In these solutions, the tetrabromocopper(II) complex was proposed to exist with a distorted planar or a pseudo tetrahedral structure. The main copper(II) complex in solution H was not a tetrabromo complex but a mixed-coordinated bromoaquacopper(II) complex in which distances for the equatorial interactions for the Cu-O and Cu-Br were 1.99A and 2.37A respectively. (author)