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In situ characterization of elusive salt hydrates : the crystal structures of the heptahydrate and octahydrate of sodium sulfate

Oswald, Iain D.H. and Hamilton, Andrea and Hall, Christopher and Marshall, William G. and Prior, Timothy J. and Pulham, Colin R. (2008) In situ characterization of elusive salt hydrates : the crystal structures of the heptahydrate and octahydrate of sodium sulfate. Journal of the American Chemical Society, 130 (52). pp. 17795-17800. ISSN 0002-7863

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    Abstract

    An important intermediate phase in the crystallization of aqueous solutions of sodium sulfate is the highly metastable sodium sulfate heptahydrate (Na2SO4·7H2O). This has been structurally characterized for the first time by in situ single crystal X-ray diffraction. The crystal structure shows that each sodium cation is octahedrally coordinated to water molecules, with a slight distortion due to one of the water molecules being disordered. The hydrated sodium cations are hydrogen-bonded to form a three-dimensional bonded network, which is markedly different from the architecture of one-dimensional bonded chains observed in sodium sulfate decahydrate (mirabilite). This major structural difference explains the reconstructive nature of the transformation observed between the heptahydrate and mirabilite. High-pressure crystallization of a 3.41 mol/kg water aqueous solution of sodium sulfate at 1.54 GPa in a diamond-anvil cell resulted in the formation of a previously unknown sodium sulfate hydrate, which we have determined by single crystal X-ray diffraction methods to be an octahydrate, Na2SO4·8H2O. In this structure the sulfate ions are coordinated directly to sodium ions. This resembles anhydrous sodium sulfate (thenardite) but contrasts with the heptahydrate and decahydrate in which the sodium ions are coordinated exclusively by water molecules. This observation demonstrates how the delicate balance of inter- and intramolecular bonds in the crystal structure can be significantly altered by the application of pressure.

    Item type: Article
    ID code: 12946
    Keywords: salt hydrates, crystal structures, heptahydrate, octahydrate, sodium sulfate, pharmacology, Pharmacy and materia medica, Therapeutics. Pharmacology, Microbiology, Biochemistry, Colloid and Surface Chemistry, Chemistry(all), Catalysis
    Subjects: Medicine > Pharmacy and materia medica
    Medicine > Therapeutics. Pharmacology
    Science > Microbiology
    Department: Faculty of Science > Strathclyde Institute of Pharmacy and Biomedical Sciences
    Professional Services > Information Services
    Related URLs:
      Depositing user: Ms Ann Barker-Myles
      Date Deposited: 26 Aug 2009 14:51
      Last modified: 28 Mar 2014 18:07
      URI: http://strathprints.strath.ac.uk/id/eprint/12946

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