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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >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.
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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.

机译：化学计量依赖的结构：反应化学计量对氰尿酸钾体系中形成的晶体产物的影响的X射线和中子单晶衍射研究。

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摘要

Reaction of cyanuric acid (C(3)H(3)N(3)O(3); neutral form CYH(3); anionic form CYH_2;-; dianionic form CYH(2-)) with K(2)CO(3) 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(CYH(2))(H(2)O)], (1), of which the crystal structure is already known [Marsh, R. E. et al. (2002). Acta Cryst. B58, 62-77], and [K(2)(CYH)], (2), a highly symmetrical and dense structure. Further stoichiometric variation produced another new complex, (3), and reaction of Rb(2)CO(3) with CYH(3) 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)(C(3)D(2)N(3)O(3))(3)(C(3)D(3)N(3)O(3))(D(2)O)(4)], the deuterated form of [K(3)(CYH(2))(3)(CYH(3))(H(2)O)(4)].
机译：氰尿酸（C（3）H（3）N（3）O（3）;中性形式CYH（3）;阴离子形式CYH_2;-;双阴离子形式CYH（2-））与K（2）CO（ 3）根据所用的反应化学计量，在水溶液中的KOH或KOH生成三种不同的结晶产物。两种产品的结构很容易通过单晶X射线衍射确定：[K（CYH（2））（H（2）O）]，（1），其中的晶体结构是已知的[Marsh，RE等。 （2002）。 Acta Cryst。 B58，62-77]和[K（2）（CYH）]，（2），高度对称且密集的结构。进一步的化学计量变化产生了另一个新的配合物（3），Rb（2）CO（3）与CYH（3）的反应产生了另一种产物（4），发现该产物与（3）是同构的。通过X射线衍射确定（3）和（4）的结构，由于电荷不平衡而导致化学上不合理的结果，该不对称单元显然含有2-对1.5+（部分电荷是结晶镜的结果）对称）。对（3）的完全氘代样品进行的单晶中子衍射分析显示，存在超细胞，与X射线结果相比，c轴增加了一倍。随后用该超级电池对结构进行的改进表明，这是仅两个D原子破坏了晶体学施加的镜面对称性的结果，否则，其余结构基本上可以观察到。 X射线衍射无法识别出与伪对称性的这种微小偏差。因此，单晶中子衍射数据表明，（3）结构的真实化学式[以及大概还具有Rb代替K和H代替D的同质结构（4）的化学式为[K（3）（ C（3）D（2）N（3）O（3））（3）（C（3）D（3）N（3）O（3））（D（2）O）（4）]， [K（3）（CYH（2））（3）（CYH（3））（H（2）O）（4）的氘代形式。

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