The crystal structure of levocetirizine dihydrochloride Form I has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Levocetirizine dihydrochloride Form I apparently crystallizes in space group P21/n (#14) with a = 24.1318(21), b = 7.07606(9), c = 13.5205(7) Å, β = 97.9803(4)°, V = 2286.38(12) Å3, and Z = 4. The crystal structure consists of interleaved double columns of cations and anions along the short b-axis. The hydrogen bonds link the cations and anions along this axis. Each protonated nitrogen atom forms a strong N–H⋯Cl hydrogen bond to one of the chloride anions. The carboxylic acid group also forms an H-bond to Cl56, resulting in a ring with a graph set R1,2(10). The centrosymmetric P21/n model for the crystal structure of levocetirizine dihydrochloride is better than the non-centrosymmetric P21 model, even though levocetirizine is a chiral molecule; the sample exhibits weak second-harmonic generation, and three weak peaks which violate the glide plane are observed. The centrosymmetric model is better by statistical, graphical, and energetic measures, as well as by chemical reasonableness. To accommodate the chiral molecule in a centrosymmetric space group, the chiral central carbon atom was disordered over two half-occupied positions, so that each cation site could be occupied by a cation of the correct chirality. A powder pattern from a Le Bail extraction of this synchrotron data set is included in the Powder Diffraction File™ as entry 00-066-1627.

中文翻译：

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左西替利嗪二盐酸盐晶型 I，C21H27ClN2O3Cl2 的晶体结构

已经使用同步加速器 X 射线粉末衍射数据解析和改进了 I 型盐酸左西替利嗪的晶体结构，并使用密度泛函技术进行了优化。左西替利嗪二盐酸盐 I 型明显在空间群中结晶磷21/n（＃14）与一种= 24.1318(21),b= 7.07606(9),C= 13.5205(7) 埃，β= 97.9803(4)°,五= 2286.38(12) Å3， 和Z= 4. 晶体结构由沿短线交错的阳离子和阴离子双柱组成b-轴。氢键沿该轴连接阳离子和阴离子。每个质子化的氮原子与一个氯阴离子形成一个强的 N-H⋯Cl 氢键。羧酸基团还与 Cl56 形成 H 键，从而形成具有图集的环R1,2(10). 中心对称磷21/n盐酸左西替利嗪晶体结构模型优于非中心对称模型磷21模型，尽管左西替利嗪是一种手性分子；样品表现出较弱的二次谐波产生，并观察到三个违反滑行平面的弱峰。通过统计、图形和能量测量以及化学合理性，中心对称模型更好。为了将手性分子容纳在中心对称空间群中，手性中心碳原子在两个半占据位置上是无序的，因此每个阳离子位点都可以被具有正确手性的阳离子占据。来自同步加速器数据集的 Le Bail 提取的粉末图案包含在 Powder Diffraction File™ 中，作为条目 00-066-1627。