An EXAFS Investigation of the Structures of Bromocopper ( II) Complexes in Some Solutions

Abstract

The structures of bromocopper (II) complexes in methanolic (M 1, M 2, M 3, M 4), 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), O.493 and 4.525 (M3), 0.260 and 4.073 (M4), 1.031 and 4.313 (E), and O.982 and 5.426 (H). In M 1 solution the interatomic distances for the Cu-O_eq, Br_eq-Cu, and Br_eq-O_eq(eq=equatorial) were 2.00A, 2.35Å, and 3.15Å respectively, and the Br_eq-Cu-O_eq, angle was estimated as about 92°. Therefore, trans-dibromo his (methanol) copper(II) complex with a slightly distorted planar structure was proposed to be dominant complex species in M 1solution. The interatomic distances in M 2, M 3, M 4 and E solutions were 2.37Å and 3.45A (average) for the Br_eq-Cu and Br_eq-Br_eq respectively. The Br_eq-Cu-Br_eqangle, paticularly in solutions M 2 and E, was estimated as about 95°. 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 mixedcoordinated bromoaquacopperan complex in which distances for the equatorial interactions for the Cu-O and Cu-Br were 1.99Åand 2.37Å respectively.