Two imidazolium hypodiphosphates, (C₃H₅N₂)(H₃P₂O₆) (I) and (C₃H₅N₂)₂(H₂P₂O₆) (II), have been synthesized and structurally characterized. In both metal‐free organic–inorganic hybrids (I) and (II), the hypodiphosphate mono‐ and dianions, (H₃P₂O₆)⁻ and (H₂P₂O₆)²⁻, form hydrogen‐bonded frameworks of different types, to which the organic cations are linked via N—H…O and C—H…O hydrogen bonds. The purity of the compounds was confirmed by powder X‐ray diffraction. Differential scanning calorimetry of compound (I) revealed two structural phase transitions: continuous at 311.8 K [cooling/heating; from high‐temperature phase (HTP) to room‐temperature phase (RTP)] and a discontinuous one at 287.9/289.2 K [RTP → low‐temperature phase (LTP)]. Compound (I) is characterized in a wide temperature range by single‐crystal and powder X‐ray diffraction methods. Crystal structures of high‐ and low‐temperature phases are determined, which show orthorhombic (HTP, Pnna, No. 52) → monoclinic (LTP, P2₁/n11, No. 14, a‐axis doubled) structural change on cooling with an intermediate incommensurately modulated phase (RTP). Dynamic properties of polycrystalline (I) were studied by means of dielectric spectroscopy. The dielectric behaviour is explained by the motion of imidazolium cations.

中文翻译：

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次磷酸咪唑鎓的晶体结构和相变

合成了两个咪唑鎓次磷酸二酯（C ₃ H ₅ N ₂）（H ₃ P ₂ O ₆）（I）和（C ₃ H ₅ N ₂）₂（H ₂ P ₂ O ₆）（II）。表征。在无金属的有机-无机杂化物（I）和（II）中，次磷酸二氢盐和二价阴离子（H ₃ P ₂ O ₆）^-和（H ₂ P ₂ O ₆）^2-，形成不同类型的氢键构架，有机阳离子通过NH-O和CHH-O氢键连接。化合物的纯度通过粉末X射线衍射确定。化合物（I）的差示扫描量热法显示两个结构相变：在311.8K [冷却/加热；从高温阶段（HTP）到室温阶段（RTP）]，并在287.9 / 289.2 K [RTP→低温阶段（LTP）]不连续。化合物（I）通过单晶和粉末X射线衍射方法在宽温度范围内表征。确定了高温和低温相的晶体结构，它们显示出斜方晶系（HTP，Pnna，52号）→单斜晶系（LTP，P 2 ₁ / n11，第14号，一个与中间incommensurately调制的相位（RTP）冷却轴加倍）的结构改变。通过介电谱研究了多晶（I）的动态性质。介电行为通过咪唑阳离子的运动来解释。