Die Kristallstrukturen der Hydrate CaI2 · 6,5 H2O und CaI2 · 4 H2O

Thiele, G.; Putzas, D.

doi:10.1002/zaac.19845191224

Cited by 18 publications

(14 citation statements)

References 12 publications

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“…The distance of 3.56 A is in good agreement with the values of 3.60 A found in an X-ray diffraction study on a concentrated aqueous NaI solution (Maeda & Ohtaki, 1975) and the 3.50 A from earlier EXAFS studies (Tanida & Watanabe, 2000). The occupancy of 10 appears to be somewhat overestimated compared to the value of 6 that was assumed in those studies, but agrees well with the 10-11 close oxygens identified in the environment of iodide ion in a X-ray crystallographic study (Thiele & Putzas, 1984). …”

Section: Resultssupporting

confidence: 88%

X-ray absorption spectroscopic studies on model compounds for biological iodine and bromine

Feiters

Küpper

Meyer‐Klaucke

2004

J Synchrotron Radiat

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We have measured the X-ray absorption spectra of a number of organic iodine and bromine compounds of biological relevance, as well as of a series of iodine compounds with different oxidation states. We find that the iodine K edge spectra (XANES) are relatively featureless but that the position of the edge is sensitive to formal valence (among other factors), and the edge shape to the number of bound oxygens. EXAFS spectra of organohalogen compounds (both iodine and bromine) can be used to discriminate between aliphatic and aromatic compounds. There are differences both in the distances from the halogens to the first shell of carbons, which are shorter for aromatic compounds, as well as in the patterns of shells in the Fourier transforms. This result is expected to be relevant to studies at these edges in biological systems.A b b r e v ia tio n s : EXAFS = extended X-ray absorption fine structure; XANES = X-ray absorption near-edge structure; XAS = X-ray absorption spectroscopy 1

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Section: Resultssupporting

confidence: 88%

X-ray absorption spectroscopic studies on model compounds for biological iodine and bromine

Feiters

Küpper

Meyer‐Klaucke

2004

J Synchrotron Radiat

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“…4a, 5a, and 5b). The structural parameters determined from the fitting (Tables 2 and 3) show close agreement with respect to crystal structure determinations and earlier EXAFS findings for the iodates [13,[16][17][18], reasonably good agreement for I 2 and CaI 2 Á4(H 2 O) [15,23], and not as good agreement for the nearest-neighbor coordination number for KI [21]. The EXAFS signal from I-I second nearest-neighbors in the KI structure was strong enough to be seen near 4.8 Å in the KI RDF (Fig.…”

Section: Standardssupporting

confidence: 69%

“…In contrast with NaI, the NaIÁ2(H 2 O) structure [22] has six-coordinated Na with four water molecules (Na-O distances ranging from 2.37 to 2.54 Å) and two I atoms (with Na-I = 3.21 and 3.26 Å). The CaI 2 Á4(H 2 O) structure [23] is comprised of elongated Ca octahedra that include two I atoms at the apices of the octahedron, where I-Ca is 3.13 Å, and four shorter equatorial water molecules at 2.30 Å from the Ca; therefore, iodine in this structure has n = 1, or one Ca atom.…”

Section: Introductionmentioning

confidence: 99%

Iodine valence and local environments in borosilicate waste glasses using X-ray absorption spectroscopy

McKeown

Muller

Pegg

2015

Journal of Nuclear Materials

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a b s t r a c tThe radioisotope 129 I, a fission product in spent nuclear fuel, has a long half-life, and can be highly mobile in the environment. Iodine K-edge X-ray absorption spectra were collected to characterize the iodine valence and coordination environment in simulated Hanford low activity waste glasses. Both iodine XANES and EXAFS data for eleven borosilicate glasses indicate iodide-like environments within the glass structure, where I À has Na or Li nearest-neighbors, and where the nearest-neighbor cation-type correlates to the most common network-modifying cation in the glass. This is further supported by the systematic increase of iodine incorporation with the combined Na 2 O + Li 2 O content in the glass. EXAFS analyses determined I-Na distances near 3.04 Å with coordination numbers near 4.0 and I-Li distances near 2.80 Å with coordination numbers near 3.0. I-Na environments determined for the glasses are similar to the tetrahedral INa 4 coordination found in NaI-sodalite. These weakly bound iodine-alkali configurations may be the only pathways for iodine to be retained in the glass. These environments may be precursors to NaI-sodalite crystallization in Na-rich glass. Iodine also shows distinct differences from chlorine in terms of the preferred sites in the glass structure.

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“…Figure S4b). 50 This structure also displays octahydrated calcium ions with the mean Ca-O distance 2.47 Å (three oxygen atoms shared between the calcium ions) and 11 second-sphere Ca‚‚‚I distances around each calcium ion in the range from 5.0 to 5.6 Å, mean value 5.30 Å.…”

Section: Laxs Resultsmentioning

confidence: 98%

Hydration of the Calcium Ion. An EXAFS, Large-Angle X-ray Scattering, and Molecular Dynamics Simulation Study

et al. 2000

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The structure of the hydrated calcium(II) ion in aqueous solution has been studied by means of extended X-ray absorption fine structure spectroscopy (EXAFS), large-angle X-ray scattering (LAXS), and molecular dynamics (MD) methods. The EXAFS data displayed a broad and asymmetric distribution of the Ca-O bond distances with the centroid at 2.46(2) A. LAXS studies on four aqueous calcium halide solutions (1.5-2 mol dm(-)(3)) gave a mean Ca-O bond distance of 2.46(1) A. This is consistent with a hydration number of 8 determined from correlations between mean distances and coordination numbers from crystal structures. The LAXS studies showed a second coordination sphere with a mean Ca.O(II) distance of 4.58(5) A, and for the hydrated halide ions the distances Cl.O 3.25(1) A, Br.O 3.36(1) A, and I.O 3.61(1) A were obtained. Molecular dynamics simulations of CaCl(2)(aq) were performed using three different Ca(2+)-OH(2) pair potentials. The potential from the GROMOS program gave results in agreement with experiments, i.e., a coordination number of 8 and an average Ca-O distance of 2.46 A, and was used for further comparisons. Theoretical EXAFS oscillations were computed for individual MD snapshots and showed very large variations, though the simulated average spectrum from 2000 snapshots gave satisfactory agreement with the experimental EXAFS spectra. The effect of thermal motions of the coordinated atoms is inherent in the MD simulation method. Thermal disorder parameters evaluated from simulated spatial atom distribution functions of the oxygen atoms coordinated to the calcium ion were in close agreement with those from the current LAXS and EXAFS analyses. The combined results are consistent with a root-mean-square displacement from the mean Ca-O distance of 0.09(2) A in aqueous solution at 300 K.

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Die Kristallstrukturen der Hydrate CaI₂ · 6,5 H₂O und CaI₂ · 4 H₂O

Cited by 18 publications

References 12 publications

X-ray absorption spectroscopic studies on model compounds for biological iodine and bromine

X-ray absorption spectroscopic studies on model compounds for biological iodine and bromine

Iodine valence and local environments in borosilicate waste glasses using X-ray absorption spectroscopy

Hydration of the Calcium Ion. An EXAFS, Large-Angle X-ray Scattering, and Molecular Dynamics Simulation Study

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