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Ion-pairing in aqueous CaCl2 and RbBr solutions : Simultaneous structural refinement of XAFS and XRD data

Pham, Van-Thai and Fulton, John L. (2013) In Journal of Chemical Physics 138(4).
Abstract

We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (x-ray absorption/diffraction structural refinement, XADSR) to study the hydration and ion pair structure of CaCl2 and RbBr salts in concentrated aqueous solutions. The XADSR method combines the x-ray absorption fine structure (XAFS) spectral analysis of both the cation and anion as a probe of their short-range structure with an x-ray diffraction (XRD) spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure, and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous... (More)

We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (x-ray absorption/diffraction structural refinement, XADSR) to study the hydration and ion pair structure of CaCl2 and RbBr salts in concentrated aqueous solutions. The XADSR method combines the x-ray absorption fine structure (XAFS) spectral analysis of both the cation and anion as a probe of their short-range structure with an x-ray diffraction (XRD) spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure, and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous CaCl2 reveals that there are ∼0.26 Ca2+-Cl- CIP's separated by about 2.71 Å, while there are 3.4 SSIP's separated by about 4.98 Å. In contrast XADSR analysis of 6 m aqueous RbBr yields about 0.7 pair CIP at a bond length of 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems.

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type
Contribution to journal
publication status
published
in
Journal of Chemical Physics
volume
138
issue
4
article number
044201
publisher
American Institute of Physics (AIP)
external identifiers
  • scopus:84873594509
ISSN
0021-9606
DOI
10.1063/1.4775588
language
English
LU publication?
no
id
094bcba5-94af-4ec7-8081-3bcc6f17a63c
date added to LUP
2019-06-30 09:45:00
date last changed
2022-01-31 22:55:42
@article{094bcba5-94af-4ec7-8081-3bcc6f17a63c,
  abstract     = {{<p>We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (x-ray absorption/diffraction structural refinement, XADSR) to study the hydration and ion pair structure of CaCl<sub>2</sub> and RbBr salts in concentrated aqueous solutions. The XADSR method combines the x-ray absorption fine structure (XAFS) spectral analysis of both the cation and anion as a probe of their short-range structure with an x-ray diffraction (XRD) spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure, and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous CaCl<sub>2</sub> reveals that there are ∼0.26 Ca<sup>2+</sup>-Cl<sup>-</sup> CIP's separated by about 2.71 Å, while there are 3.4 SSIP's separated by about 4.98 Å. In contrast XADSR analysis of 6 m aqueous RbBr yields about 0.7 pair CIP at a bond length of 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems.</p>}},
  author       = {{Pham, Van-Thai and Fulton, John L.}},
  issn         = {{0021-9606}},
  language     = {{eng}},
  month        = {{01}},
  number       = {{4}},
  publisher    = {{American Institute of Physics (AIP)}},
  series       = {{Journal of Chemical Physics}},
  title        = {{Ion-pairing in aqueous CaCl<sub>2</sub> and RbBr solutions : Simultaneous structural refinement of XAFS and XRD data}},
  url          = {{http://dx.doi.org/10.1063/1.4775588}},
  doi          = {{10.1063/1.4775588}},
  volume       = {{138}},
  year         = {{2013}},
}