Bromine-oxygen radial distribution functions [g(r)] have been calculated by means of molecular dynamics simulations for aqueous solutions of rubidium bromide, 2-bromopropane and bromoethane. X-ray absorption spectra at the bromine K edge have been recorded for these solutions. The water contribution to the extended x-ray absorption fine structure spectra has been calculated Starting from the g&O (r) distribution function. Fits of the x-ray absorption spectra have been performed directly on the raw experimental data, allowing the reliability of the g(r) distribution functions to be verified. The agreement between theoretical and experimental spectra is satisfactory. A procedure to improve model g(r) functions on the basis of the short-range structural information provided by extended x-ray absorption fine structure data is proposed.

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The structures of the mono-, bis-, and tris(glycinato)copper(II) complexes in aqueous solution have been determined by X-ray absorption spectroscopy. Four solutions with different complex ratios have been examined, and the species concentrations have been determined on the basis of complex stability constants. An advanced data analysis including multiple-scattering effects and multielectron excitation processes produced quantitative information on the Cu(II)-glycinate complexes present in aqueous solution. The structure of the bis(glycinato)copper(II) complex, which has a low solubility in water, has been determined for the first time. It has been found to have a distorted octahedral geometry with two bidentate glycine ligands coordinating to the Cu 2+ ion in the equatorial plane and with the axial sites occupied by two additional water molecules at 2.40 ( 0.06 Å. Analysis of the X-ray absorption data allowed a detailed description of the structures of the mono-and tris(glycinato)copper(II) species. The former complex has an axially elongated octahedral structure with a glycine bidentate ligand and two water molecules placed at the equatorial and two water molecules at the axial positions (2.44 ( 0.08 Å). Experimental data for the latter complex were also explained in terms of a distorted octahedral model with two glycine molecules in the equatorial plane and with the amino nitrogen of the third glycine coordinating to the Cu 2+ ion at the axial site at a distance of 2.33 ( 0.05 Å. This result conflicts with the regular octahedral geometry previously determined by XRD investigations. The axial bonds of the three complexes are significatively longer than the average within the hexaaquocopper-(II) ions. This finding indicates that the axial bonds are lengthened upon the formation of the Cu-glycine complexes and the Cu(II)-water interaction at the axial site is weakened.

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The local environment of the Cu2+ ion in copper chloride solutions has been investigated by x-ray absorption spectroscopy. Three aqueous solutions of CuCl2 with increasing Cl−/Cu2+ ratio have been examined. An advanced data analysis including multiple-scattering effects produced quantitative information on the chlorocuprate complexes present in solution and provided evidence for an increasing degree of complex formation between Cu2+and Cl− ions with increasing chloride concentration. The presence of Cu–Cl interactions at the axial site has been detected in a 0.1 M CuCl2 solution for the first time. At higher chloride concentrations (Cl−/Cu2+ratios equal 10 and 30) the equatorial positions in the distorted octahedral copper coordination are occupied by 3.2 and 3.0 oxygens and 0.8 and 1.0 chloride ions, respectively, while the axial positions are occupied by 1.2 and 1.0 oxygens and 0.8 and 1.0 chloride ions, respectively. The results are found to be consistent with previous x-ray and neutron diffraction studies and with experimental data on the complex formation. © 1997 American Institute of Physics