Hydrogen-Bonded Displacive-Type Ferroelastic Phase Transition in a New Entangled Supramolecular Compound

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• 作者：Yuanyuan Tang ; Zhihua Sun ; Chengmin Ji ; Lina Li ; Shuquan Zhang ; Tianliang Chen ; Junhua Luo
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：January 7, 2015
• 年：2015
• 卷：15
• 期：1
• 页码：457-464
• 全文大小：530K
• ISSN：1528-7505

文摘

The framework entanglements show structural transitions by the removal and incorporation of guest molecules, but rarely generate phase transitions by themselves. In this study, we report a new entangled hydrogen-bonded supramolecular compound, [(n-C₄H₉)₂NH₂]₂H₂C₄O₄路H₄C₄O₄ (1, H₄C₄O₄ = fumaric acid), which undergoes a reversible ferroelastic phase transition with the Aizu notation of 2/mF1虆. Differential scanning calorimetry and specific heat measurements confirm its typical second-order phase transition at around 228.8 K (T_c), while the results of the deuterated analogue (2) are different with those of 1, indicating that proton dynamic motions in hydrogen bonds contribute to the phase transition. Variable-temperature single-crystal X-ray diffraction analyses reveal that the cooperative displacements of hydrogen bonds induce the structural phase transition, which arise from the twisting motions of the fumaric acid molecules. Simultaneously, two types of independent hydrogen bonding layers in the entanglement are altered in response to the transformation of hydrogen bonds aggregates at the low temperature phase, causing the symmetry breaking. These findings will open up a new avenue for the design of ferroic materials with an entangled framework.