A Mechanism for Reversible Solid-State Transitions Involving Nitro Torsion
A Mechanism for Reversible Solid-State Transitions Involving Nitro Torsion
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DOI：
10.1021/acs.chemmater.0c02209
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发表时间：
2020-09-22
影响因子：
8.6
通讯作者：
Yu, Lian
中科院分区：
文献类型：
--
作者：
Gui, Yue;Yao, Xin;Yu, Lian
可逆固相转变在刺激响应型材料中很重要。目前的理解局限于什么样的结构可以实现可逆的转变。我们报道，对于含有硝基的分子固体，如果硝基是氢键(HB)受体并且具有扭转自由度，则可以发生可逆相变。我们使用硝苯地平(NIF)的多晶型来解释这一现象，利用它们不同的分子堆积但化学结构相同的优势。NIF有6个已知的晶型，其中4个在100K时动力学稳定，其中两个晶型在加热时经历了可逆的相变，体积变化很大，而其他的则不是。在转化结构中，硝基是HB受体，并旋转以优化HBs以抵消紧密堆积的损失，而在非活性结构中，硝基具有类似的扭转自由度，但不参与HBs。我们使用剑桥结构数据库中所有可用的系统，包括NIF的衍生物尼索地平，测试了这种现象的普遍性，并提出了在设计具有受控机械响应的材料方面的可能应用。
Reversible solid-state transformations are important in stimuli-responsive materials. The current understanding is limited on what kind of structure enables reversible transitions. We report that for molecular solids containing nitro groups, reversible phase transitions can occur if the nitro group is a hydrogen bond (HB) acceptor and has torsional freedom. We use the polymorphs of nifedipine (NIF) to illustrate this phenomenon taking advantage of their different molecular packing but identical chemical structure. NIF has six known polymorphs with four being kinetically stable at 100 K. Upon heating, two polymorphs undergo reversible phase transitions with large volume change, while the others do not. In the transforming structures, the nitro group is an HB acceptor and rotates to optimize HBs to offset loss of close packing, while in the inactive structures, the nitro group has similar torsional freedom but is not engaged in HBs. We test the generality of this phenomenon using all available systems in the Cambridge Structural Database, including NIF's derivative nisoldipine, and suggest possible applications in designing materials with controlled mechanical response.