In situ characterization of elusive salt hydrates. The crystal structures of the heptahydrate and octahydrate of sodium sulfate.
In situ characterization of elusive salt hydrates. The crystal structures of the heptahydrate and octahydrate of sodium sulfate.
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DOI：
10.1021/ja805429m
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发表时间：
2008-11
影响因子：
15
通讯作者：
I. Oswald;A. Hamilton;C. Hall;W. G. Marshall;T. Prior;C. Pulham
中科院分区：
文献类型：
--
作者：
I. Oswald;A. Hamilton;C. Hall;W. G. Marshall;T. Prior;C. Pulham
硫酸钠水溶液结晶中的一个重要中间相是高度亚稳的七水硫酸钠（Na（2）SO（4）.7H（2）O）。这已在结构上的特点是第一次在原位单晶X射线衍射。晶体结构显示，每个钠阳离子与水分子八面体配位，由于其中一个水分子无序而略有扭曲。水合钠阳离子通过氢键形成三维键合网络，这与十水硫酸钠（芒硝）中观察到的一维键合链的结构明显不同。这种主要的结构差异解释了七水合物和芒硝之间观察到的转化的重建性质。在金刚石压砧室中，在1.54 GPa下，3.41 mol/kg硫酸钠水溶液的高压结晶导致形成先前未知的硫酸钠水合物，我们已经通过单晶X射线衍射方法确定其为八水合物Na（2）SO（4）.8H（2）O。在这种结构中，硫酸根离子直接与钠离子配位。这类似于无水硫酸钠（芒硝），但与钠离子仅由水分子配位的七水合物和十水合物形成对比。这一观察结果表明，晶体结构中分子间和分子内键的微妙平衡如何通过施加压力而显着改变。
An important intermediate phase in the crystallization of aqueous solutions of sodium sulfate is the highly metastable sodium sulfate heptahydrate (Na(2)SO(4).7H(2)O). 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, Na(2)SO(4).8H(2)O. 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.