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.
Composition and existence range of aggregates formed by sodium taurodeoxycholate in aqueous micellar solutions were studied. Electromotive force measurements provide the free concentration of hydrogen and sodium ions. Solubility measurements of barium taurodeoxycholate give that of taurodeoxycholate ions. Experimental data obtained at 25 °C and at seven different concentrations of N(CH3)4Cl, used as an ionic medium, can be explained by assuming the presence of aggregates with different composition depending on the concentration of the reagents and the ionic strength. The comparison with deoxycholate and glycodeoxycholate shows analogies and differences. Protonated species were observed only at pH approximately less than 8.3. At pH's within the range 8.3−10 the distribution of the micellar aggregates remains nearly constant at a given ionic medium concentration. As it is expected, the size of the micellar aggregates increases upon increasing the ionic strength. A trimer was found for all the concentrations of the ionic medium. Most of the species found have aggregation numbers of the anion that are multiples of 3. It can be supposed that the trimer may be the fundamental unit of the structure of the micellar aggregates. An appreciable amount of a dimer, if any, was not detected. The affinity of sodium ions for the micellar aggregates is greater than that of N(CH3)4 + ions. The charge density of the micellar aggregates was determined to be low.
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
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.