State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
J Phys Chem B. 2011 Jul 28;115(29):8981-8. doi: 10.1021/jp202975q. Epub 2011 Jul 7.
We report the results of high-pressure Raman and X-ray diffraction measurements performed on ammonium squarate ((NH(4))(2)C(4)O(4), AS), a representative supramolecular architecture based on hydrogen bonding and π-stacking interactions, at various pressures up to 19 GPa. Two phase transitions at ∼2.7 GPa and in the pressure range of 11.1-13.6 GPa were observed. Both Raman and XRD results provide convincing evidence for these two phase transitions. The first phase transition is attributed to the rearrangements of hydrogen-bonding networks, resulting in the symmetry transformation from P2(1)/c to P1. The second one, which is identified as an order-disorder phase transition, arises from significant modifications of squarate rings and random orientations of NH(4)(+) cations. The cooperative effects between hydrogen-bonding and π-stacking interactions, as well as mechanisms for the phase transitions, are discussed by virtue of the local structure of AS.
我们报告了在高达 19 GPa 的各种压力下对基于氢键和π-堆积相互作用的代表性超分子结构草酰胺铵（(NH(4))(2)C(4)O(4)，AS）进行高压拉曼和 X 射线衍射测量的结果。在约 2.7 GPa 和 11.1-13.6 GPa 的压力范围内观察到了两个相变。拉曼和 XRD 结果都为这两个相变提供了令人信服的证据。第一个相变归因于氢键网络的重新排列，导致从 P2(1)/c 到 P1 的对称转变。第二个相变被确定为有序-无序相变，它源于草酰胺环的显著修饰和 NH(4)(+)阳离子的随机取向。通过 AS 的局部结构讨论了氢键和π-堆积相互作用之间的协同效应以及相变机制。
