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

Iain D.H. Oswald, Andrea Hamilton, Christopher Hall, William G. Marshall, Timothy J. Prior, Colin R. Pulham

Research output: Contribution to journalArticle

27 Citations (Scopus)

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.
LanguageEnglish
Pages17795-17800
Number of pages6
JournalJournal of the American Chemical Society
Volume130
Issue number52
Early online date24 Nov 2008
DOIs
Publication statusPublished - 24 Nov 2008

Fingerprint

Sodium sulfate
Hydrates
Salts
Crystal structure
Sodium
Water
Molecules
Ions
Crystallization
X-Ray Diffraction
Positive ions
Cations
Single crystals
X ray diffraction
Pressure
Diamond
sodium sulfate
Diamonds
Sulfates
Hydrogen

Keywords

  • salt hydrates
  • crystal structures
  • heptahydrate
  • octahydrate
  • sodium sulfate
  • pharmacology

Cite this

Oswald, Iain D.H. ; Hamilton, Andrea ; Hall, Christopher ; Marshall, William G. ; Prior, Timothy J. ; Pulham, Colin R. / In situ characterization of elusive salt hydrates : the crystal structures of the heptahydrate and octahydrate of sodium sulfate. In: Journal of the American Chemical Society. 2008 ; Vol. 130, No. 52. pp. 17795-17800.
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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.; Hamilton, Andrea; Hall, Christopher; Marshall, William G.; Prior, Timothy J.; Pulham, Colin R.

In: Journal of the American Chemical Society, Vol. 130, No. 52, 24.11.2008, p. 17795-17800.

Research output: Contribution to journalArticle

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N2 - 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.

AB - 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.

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