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Lookup NU author(s): Gary Nichol, Professor William Clegg
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-5-5-hydroxyhydurilato] hemihydrate], {[Cs(C8H5N4O7)]ยท0.5H2O}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.
Author(s): Nichol G, Clegg W
Publication type: Article
Publication status: Published
Journal: Acta Crystallographica C: Crystal Structure Communications
Year: 2005
Volume: 61
Issue: 10
Pages: m459-m462
Date deposited: 09/10/2007
ISSN (print): 0108-2701
ISSN (electronic): 1600-5759
Publisher: Wiley-Blackwell Munksgaard
URL: http://journals.iucr.org/c/issues/2005/10/00/sk1870/index.html
