The solid-state behavior of two organic zwitterions, (Z)-3-carboxy-2-(4-cyanopyridin-1-ium-1-yl)-acrylate (1) and (Z)-1-(3-carboxy-1,1-dihydroxyprop-2-en-1-ide-2-yl)-pyridin-1-ium (2), has been extensively investigated. Variation of crystallization conditions resulted in the identification of two conformational polymorphs of 1, a kinetic and thermodynamic form. Three polymorphs of 2, where the formation of a particular polymorph depends entirely on solvent of crystallization, were also identified. The relationship between the polymorphs of both 1 and 2 has been extensively studied, and attempts were made to interconvert between forms to determine their relative stability. No interconversion between polymorphs is observed in either 1 or 2. In the case of 1, this is likely due to restrictions on rotation of the carboxylic group in the solid state, which is required for conversion between polymorphs.

中文翻译：

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两种有机两性离子的多态行为：两种罕见的情况之间没有可观察到的多晶型转换

两种有机两性离子的固态行为（Z）-3-羧基-2-（4-氰基吡啶-1-基-1-基）丙烯酸酯（1）和（Z）-1-（3-羧基- 1,1-二羟基丙-2-烯-1-基-2-基）-吡啶-1-鎓（2）已被广泛研究。结晶条件的变化导致鉴定了两个构象多晶型物1，分别是动力学形式和热力学形式。还确定了3个2的多晶型物，其中特定多晶型物的形成完全取决于结晶溶剂。1和2的多态之间的关系已经进行了广泛的研究，并尝试在形式之间进行相互转换以确定它们的相对稳定性。在1或2中都没有观察到多态之间的相互转换。在1的情况下，这可能是由于对固态的羧基旋转的限制，这对于多晶型物之间的转化是必需的。