Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2019 Mar 14;150(10):104502. doi: 10.1063/1.5063588.
Metal-organic frameworks (MOFs) represent an important class of materials. Careful selection of building blocks allows for tailoring of the properties of the resulting framework. The self-assembly process, however, is not understood, and without detailed knowledge of the underlying molecular mechanism, it is difficult to anticipate whether a particular design can be realized, or whether the material adopts a metastable, kinetically arrested state. We present a detailed examination of early-stage self-assembly pathways of the MOF-5. Enhanced sampling techniques are used to model a self-assembly in an explicit solvent (dimethylformamide, DMF). We identify several free energy barriers encountered during the assembly of the final MOF, which arise from structural rearrangements preceding MOF formation and from disrupted MOF-solvent interactions as formation proceeds. In all cases considered here, MOFs exhibit favorable entropic gains during the assembly. More generally, the strategy presented provides a step toward the experimental design characterizing the formation of ordered frameworks and possible sources of polymorphism.
金属-有机骨架（MOFs）是一类重要的材料。通过仔细选择构建块，可以对所得骨架的性质进行定制。然而，自组装过程尚未被理解，而且如果没有对基础分子机制的详细了解，就很难预测特定设计是否可以实现，或者材料是否采用亚稳、动力学捕获状态。我们对 MOF-5 的早期自组装途径进行了详细研究。增强采样技术用于在显式溶剂（二甲基甲酰胺，DMF）中模拟自组装。我们确定了在最终 MOF 组装过程中遇到的几个自由能势垒，这些势垒来自于 MOF 形成之前的结构重排，以及随着形成的进行，MOF-溶剂相互作用的破坏。在所有考虑的情况下，MOFs 在组装过程中表现出有利的熵增益。更一般地，所提出的策略为实验设计提供了一个方向，用于表征有序框架的形成和可能的多晶型来源。
