The reaction of Cd(NO₃)₂·4H₂O and 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide (H₂LBr) under different reaction conditions generates two pseudopolymorphs, {[Cd(L)₂]·2H₂O}⊃C₃H₆O (1α) and {[Cd(L)₂]·2H₂O}⊃3H₂O (1β). Crystal structure analysis reveals that complexes 1α and 1β feature an essentially identical 1D metallacyclic chain structure, and their structural differences mainly stem from different packing modes of the identical 2D sheets, consisting of identical 1D metallacyclic chains linked via π⋯π interactions. Corresponding to the different packing modes, complexes 1α and 1β have distinctly different space groups: the acentric orthorhombic space group Fdd2 for 1α and the centric monoclinic space group I2/c for 1β. For acentric 1α crystals, modest powder second-harmonic-generation (SHG) efficiency is observed at room temperature.

中文翻译：

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基于一维金属双环链的伪多态性，该链由两性离子双位二酸二酸有机连接剂构成

Cd（NO ₃）₂ ·4H ₂ O与4-羧基-1-（4-羧基苄基）溴化吡啶鎓（H ₂ LBr）在不同反应条件下的反应生成两个假多晶型，{[Cd（L）₂ ]·2H ₂ ö}⊃C ₃ ħ ₆ O（1α）和{[CD（L）₂ ]·2H ₂ ö}⊃3H ₂ O（1β）。晶体结构分析表明复合物1α和1β具有基本相同的一维金属环链结构，并且它们的结构差异主要源于相同的2D片材的不同堆积模式，该填充模式由通过π⋯π相互作用连接的相同的一维金属环链组成。对应于不同的包装模式，复合物1α和1β具有明显不同的空间群：所述偏心正交空间群FDD 2 1α和中心斜空间群我2 / ç为1β。对于无心1α晶体，在室温下观察到适度的粉末二次谐波生成（SHG）效率。