Acta Crystallographica Section C

Crystal Structure Communications

Volume 61, Part 10 (October 2005)

metal-organic compounds

sk1870 scheme

Acta Cryst. (2005). C61, m459-m462 [ doi:10.1107/S0108270105029318 ]

Polymorphism in an unexpected caesium complex of 5-hydroxyhydurilic acid

G. S. Nichol and W. Clegg

Abstract: 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- [mu] ₅-5-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.

Formula: Two polymorphs of [Cs(C₈H₅N₄O₇)]·0.5H₂O


	Structure factor file (CIF format) (127.4 kbytes) Contains datablock I

	Structure factor file (CIF format) (135.9 kbytes) Contains datablock II

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