Nichol Gary S, Clegg William
School of Natural Sciences (Chemistry), Bedson Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, England.
Acta Crystallogr C. 2005 Oct;61(Pt 10):m459-62. doi: 10.1107/S0108270105029318. Epub 2005 Sep 30.
Vigorous reaction of barbituric acid with caesium hydroxide in water resulted in an unexpected coupling product, 5-hydroxyhydurilic acid, complexed to caesium, giving poly[[caesium-mu5-5-hydroxyhydurilato] hemihydrate], {[Cs(C8H5N4O7)].0.5H2O}n. This was obtained in two different polymorphic forms, depending on the method of crystal growth. Slow solvent evaporation yielded an orthorhombic polymorph, (I), which crystallized in the space group Pnab (non-standard setting of Pbcn), with the uncoordinated water molecule lying on a crystallographic twofold axis. The water molecule is sandwiched into cavities within the structure and is securely held in place by N-HO and O-HO hydrogen bonding. Polymorph (II) is monoclinic, although the unit-cell parameters are similar to those of polymorph (I), and it crystallizes in the space group C2/c, with the uncoordinated water molecule again lying on the twofold axis and secured by hydrogen bonding. The differences between the two polymorphs, both of which have nine-coordinate caesium and a similar first-shell environment of all structural components, are in the overall arrangement of the cations, anions and water molecules, and in the shape of the cavities, revealed by inspecting and comparing crystal-packing diagrams.
巴比妥酸与氢氧化铯在水中剧烈反应生成了一种意想不到的偶联产物5-羟基海因酸，它与铯形成配合物，得到聚[[铯-μ5-5-羟基海因酸根]半水合物]，{[Cs(C₈H₅N₄O₇)].0.5H₂O}ₙ。根据晶体生长方法的不同，该产物有两种不同的多晶型形式。缓慢溶剂蒸发得到正交晶系多晶型物（I），它在空间群Pnab（Pbcn的非标准设置）中结晶，未配位的水分子位于一个晶体学二重轴上。水分子夹在结构内的空穴中，并通过N-HO和O-HO氢键牢固地固定在原位。多晶型物（II）是单斜晶系，尽管其晶胞参数与多晶型物（I）相似，它在空间群C2/c中结晶，未配位的水分子同样位于二重轴上并通过氢键固定。通过检查和比较晶体堆积图可知，这两种多晶型物的差异在于阳离子、阴离子和水分子的整体排列以及空穴的形状，二者均具有九配位的铯且所有结构组分的第一配位层环境相似。
