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Stoichiometry-dependent structures: An X-ray and neutron single-crystal diffraction study of the effect of reaction stoichiometry on the crystalline products formed in the potassium-cyanurate system

Lookup NU author(s): Gary Nichol, Emeritus Professor Bill Clegg, Duncan Tooke

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Abstract

Reaction of cyanuric acid (C3H3N3O 3; neutral form CYH3; anionic form CYH2-; dianionic form CYH2-) with K 2CO3 or KOH in aqueous solution gave three different crystalline products, according to the reaction stoichiometry used. The structures of two products were easily determined by single-crystal X-ray diffraction: [K(CYH2)(H2O)], (1), of which the crystal structure is already known [Marsh, R. E. et al. (2002). Acta Cryst. B58, 62-77], and [K2(CYH)], (2), a highly symmetrical and dense structure. Further stoichiometric variation produced another new complex, (3), and reaction of Rb2CO3 with CYH3 yielded a further product, (4), which was found to be isostructural with (3). Determination of the structures of (3) and (4) by X-ray diffraction gave a result that was chemically unreasonable owing to a charge imbalance, with the asymmetric unit apparently containing 2- against 1.5+ (partial charges as the result of crystallographic mirror symmetry). A single-crystal neutron diffraction analysis carried out on a fully deuterated sample of (3) revealed the presence of a supercell, with the c axis doubled compared with the X-ray result. Subsequent refinement of the structure with this supercell showed that it is the result of just two D atoms breaking crystallographically imposed mirror symmetry, which is otherwise essentially observed by the rest of the structure. This minor deviation from pseudo-symmetry could not be identified by X-ray diffraction. Thus, single-crystal neutron diffraction data revealed that the true chemical formula of the structure of (3) [and presumably also of the isostructural (4) with Rb instead of K and H instead of D], is [K 3(C3D2N3O3) 3(C3D3N3O3)(D 2O)4], the deuterated form of [K3(CYH 2)3(CYH3)(H2O)4]. © 2006 International Union of Crystallography Printed in Great Britain - all rights reserved.


Publication metadata

Author(s): Nichol GS, Clegg W, Gutmann MJ, Tooke DM

Publication type: Article

Publication status: Published

Journal: Acta Crystallographica Section B: Structural Science

Year: 2006

Volume: 62

Issue: 5

Pages: 798-807

ISSN (print): 0108-7681

ISSN (electronic): 1600-5740

Publisher: Wiley-Blackwell

URL: http://dx.doi.org/10.1107/S0108768106025171

DOI: 10.1107/S0108768106025171


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