Flexibility of zeolitic imidazolate framework structures studied by neutron total scattering and the reverse Monte Carlo method
Flexibility of zeolitic imidazolate framework structures studied by neutron total scattering and the reverse Monte Carlo method
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DOI：
10.1088/0953-8984/25/39/395403
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发表时间：
2013-10-02
影响因子：
2.7
通讯作者：
Cheetham, A. K.
中科院分区：
文献类型：
--
作者：
Beake, E. O. R.;Dove, M. T.;Cheetham, A. K.
沸石咪唑酯骨架 ZIF-4 在约 600 K 时发生非晶化转变，然后在约 700 K 时转变为 ZIF-zni，这是最致密的结晶 ZIF。这一系列的远程结构重排必然会导致局部结构发生一系列相应的变化，但这些变化以前没有被直接研究过。通过逆蒙特卡罗建模分析中子总衍射数据，我们评估了该系列的柔性变化，确定了 ZIF-4 和非晶相柔性的关键模式。我们表明，ZnN4 四面体保持相对刚性，尽管不如硅酸盐中的 SiO4 四面体。然而，与硅酸盐网络相比，咪唑配体提供的额外自由度在相之间变化很大，其中配体平面外的扭转运动在非晶相中尤其重要。我们的结果进一步证明了反向蒙特卡罗模拟用于研究固体中分子间相互作用的可行性，即使在 ZIF 等配对分布函数由分子内峰主导的情况下也是如此。
The zeolitic imidazolate framework ZIF-4 undergoes an amorphization transition at about 600 K, and then transforms at about 700 K to ZIF-zni, the densest of the crystalline ZIFs. This series of long-range structural rearrangements must give a corresponding series of changes in the local structure, but these have not previously been directly investigated. Through analysis of neutron total diffraction data by reverse Monte Carlo modelling, we assess the changes in flexibility across this series, identifying the key modes of flexibility within ZIF-4 and the amorphous phase. We show that the ZnN4 tetrahedra remain relatively rigid, albeit less so than SiO4 tetrahedra in silicates. However, the extra degrees of freedom afforded by the imidazolate ligand, compared to silicate networks, vary substantially between phases, with a twisting motion out of the plane of the ligand being particularly important in the amorphous phase. Our results further demonstrate the feasibility of reverse Monte Carlo simulations for studying intermolecular interactions in solids, even in cases, such as the ZIFs, where the pair distribution function is dominated by intramolecular peaks.