Solvated EXAFS study

EXAFS studies on tris-maltolatoiron(III) in the solid state and in solution, and on [Fe(Ll)3] hydrate, pave the way for detailed investigation of the hydration of complexes of this type in aqueous media.Solubilities and transfer chemical potentials have been determined for tris-maltolatoiron(III) in methanol-water, and for tris-etiwlmaltolatoiron(III) in alcohol-water mixtures and in isobutanol, 1-hexanol, and 1-octanol. Solubility maxima in mixed solvents, indicating synergic solvation, is relevant to trans-membrane transport of complexes of this type. Solubilities of tris-ethylmaltolatoiron(III) and of [Fe(Ll)3] have been determined in aqueous salt solutions (alkali halides NH4 and NR4 bromides). ... 

Seward, TM, Henderson, CMB, Chamock, JM (2000) Indium (111) chloride complexing and solvation in hydrothermal solutions to 350° C, an EXAFS study. Chem Geol 167 117-127. 

Seward TM, Henderson CMB, Chamock JM, Driesner T (1999) An EXAFS study of solvation and ion pairing in aqueous strontium solutions to 300°C. Geochim Cosmochim Acta 63 2409-2418... 

Connick and Alder applied molecular modeling to attempt to understand the nature of the exchange process in the Ni(OH2)5 system. Merbach and co-workers used Monte Carlo simulations for lanthanide ions to predict solvation numbers for these ions and found that the calculations predicted a dissociative mechanism for the nine-coordinate ions. Calculations such as these will benefit from the extensive structural information available from EXAFS studies that has been compiled and reviewed by Ohtaki and Radnai. ... 

The solid state C nmr spectra of [Mg(Anth) (THF)jxLbI n=l, Lgj=>TMED suggest Mg is bonded to C9 and Ciq. A review of crystal structures of organomagneslum compounds has been published. LAXS and EXAFS studies have shown that RMgX (R>BMe, Et or Ph X=6r or 1 exists in EtxO as tetrasolvated monomers, [RMgXCEtiO ], and as solvated dimers [(EtiO)2RMg(p-... 

Some gold(I) derivatives have been obtained with other type of /V-donor ligands as acetonitrile the compound [Au(NCMe)2]+ can be obtained by halide-catalyzed electrolysis of gold metal in MeCN.2412 This cation is very moisture sensitive and thermally labile, but the more stable cation [Au(NCPh)2]+ has been obtained by oxidation of gold with the nitrosyl cation in benzonitrile.2413 From EXAFS spectroscopic studies it has been suggested that the solvated gold(I) cations are tetra-coordinate in pyridine or acetonitrile solutions.2414 Other gold(I) complexes have been... 

In order to gain information on the environments of certain atoms in dissolved species, in melts or in solids (crystalline or noncrystalline), which are not accessible to diffraction studies for one reason or another, X-ray absorption spectrometry (XAS) can be applied, with the analysis of the X-ray absorption near-edge structure (XANES) and/or the extended X-ray absorption fine structure (EXAFS). Surveys of these methods are available 39,40 a representative study of the solvation of some mercury species, ElgX2, in water and dimethylsulfoxide (DMSO) by EXAFS and XANES, combined with quantum-chemical calculations, has been published.41... 

Several quantum-chemical studies have been performed on Hg(CN)2 and related species, applying different approaches with consideration of relativistic effects in order to get MO schemes and energies as a basis for discussion of bonding, valence XPS,105 UPS,106 XANES and EXAFS spectra.41 The latter study also showed Hg(CN)2 to be dissolved in H20 in molecular form (/-(Hg—C) 202, r(C—N) 114 pm), and obviously not to be hydrated, a remarkable finding insofar as solvates of Hg(CN)2 with various donor molecules are well known.2 However, in contrast to Cd(CN)2 (see above), Hg(CN)2 as such does not form clathrates. 

A primary hydration number of 6 for Fe + in aqueous (or D2O) solution has been indicated by neutron diffraction with isotopic substitution (NDIS), XRD, 16,1017 EXAFS, and for Fe " " by NDIS and EXAFS. Fe—O bond distances in aqueous solution have been determined, since 1984, for Fe(H20)/+ by EXAFS and neutron diffraction, for ternary Fe " "-aqua-anion species by XRD (in sulfate and in chloride media, and in bromide media ), for Fe(H20)g by neutron diffraction, and for ternary Fe -aqua-anion species. The NDIS studies hint at the second solvation shell in D2O solution high energy-resolution incoherent quasi-elastic neutron scattering (IQENS) can give some idea of the half-lives of water-protons in the secondary hydration shell of ions such as Fe aq. This is believed to be less than 5 X I0 s, whereas t>5x10 s for the binding time of protons in the primary hydration shell. X-Ray absorption spectroscopy (XAS—EXAFS and XANES) has been used... 

During the last two decades, studies on ion solvation and electrolyte solutions have made remarkable progress by the interplay of experiments and theories. Experimentally, X-ray and neutron diffraction methods and sophisticated EXAFS, IR, Raman, NMR and dielectric relaxation spectroscopies have been used successfully to obtain structural and/or dynamic information about ion-solvent and ion-ion interactions. Theoretically, microscopic or molecular approaches to the study of ion solvation and electrolyte solutions were made by Monte Carlo and molecular dynamics calculations/simulations, as well as by improved statistical mechanics treatments. Some topics that are essential to this book, are included in this chapter. For more details of recent progress, see Ref. [1]. 

X-ray and neutron diffraction methods and EXAFS spectroscopy are very useful in getting structural information of solvated ions. These methods, combined with molecular dynamics and Monte Carlo simulations, have been used extensively to study the structures of hydrated ions in water. Detailed results can be found in the review by Ohtaki and Radnai [17]. The structural study of solvated ions in lion-aqueous solvents has not been as extensive, partly because the low solubility of electrolytes in 11011-aqueous solvents limits the use of X-ray and neutron diffraction methods that need electrolyte of -1 M. However, this situation has been improved by EXAFS (applicable at -0.1 M), at least for ions of the elements with large atomic numbers, and the amount of data on ion-coordinating atom distances and solvation numbers for ions in non-aqueous solvents are growing [15 a, 18]. For example, according to the X-ray diffraction method, the lithium ion in for-mamide (FA) has, on average, 5.4 FA molecules as nearest neighbors with an... 

Solvation structures of Br ion dissolved in 23 solvents have been studied at the Br K-edge using extended X-ray absorption fine structure (EXAFS). The results are summarized... 

Structure of Br may not be the same as that of the bulk. Some of the molecular dynamics calculations predict that halide anions in water tend to float on the surface of clusters consisting of water molecules rather than within water. This effect may cause a dissimilar solvation structure to that of the bulk. In addition, if the anion is segregated at the surface by surfactants such as large alkylammonium cations, the anion density at the surface should be high and its environment differ from the bulk. This is a preliminary report of the first experimental study of the solution surface by the EXAFS technique. This technique provides us information on the gas/liquid interface, the structure of Langmuir films, and the effect of the interface on chemical reactions. 

Modern techniques of studying solvation AXD diffraction and EXAFS... 

In the EXAFS technique the incident X-rays are absorbed by the atom which is being studied. In doing so they interact directly with the electrons of the atom and the excited electrons then probe the immediate environment of the atom. As a result X-rays are emitted and this appears as fine strucmre in an absorption. From this it is possible to deduce coordination numbers, geometry and mean distances of the atom under study to its nearest neighbours, i.e. to give information about the primary solvation of an ion. Recently it has proved useful in probing the secondary solvation shell. 

Inada Y, Sugimoto K, Ozutsumi K, Funahashi S (1994) Solvation structures of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and indium(III) ions in 1,1,3,3-tetramethylurea as studied by EXAFS and electronic spectroscopy. Variation of coordination number. Inorg Chem 33 1875-1880... 

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