Terranova Zachary L, Paesani Francesco
Department of Chemistry and Biochemistry, University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093, USA.
Phys Chem Chem Phys. 2016 Mar 21;18(11):8196-204. doi: 10.1039/c5cp07681a.
The effects of framework flexibility on the structural and dynamical properties of water adsorbed in two prototypical metal-organic frameworks are investigated through molecular dynamics simulations. It is found that water molecules in the pores of a flexible model of [Zn(l-L)(Cl)] exhibit slower dynamics than when the framework is artificially held rigid in the simulations. In contrast, the water dynamics in Co-MOF-74 is predicted to be accelerated by the framework vibrations. The origin of this different behavior directly relates to how water interacts with the two frameworks, which, in turn, determines different hydrogen-bond patterns in the pores. While the first water molecules adsorbed in [Zn(l-L)(Cl)] donate a single hydrogen bond to the Zn-Cl groups and point the other hydrogen atom towards the center of the pore, water molecules adsorbed in Co-MOF-74 initially bind to the cobalt atoms of the framework via their oxygen atoms, thus leaving each molecule free to form two hydrogen bonds with additional molecules adsorbed at higher loading. The simulation results indicate that taking into account the framework flexibility in computer simulations is necessary for a quantitative modeling of adsorption and transport processes in metal-organic frameworks.
通过分子动力学模拟研究了骨架柔性对吸附在两种典型金属有机骨架中的水的结构和动力学性质的影响。研究发现，在[Zn(l-L)(Cl)]柔性模型的孔中的水分子动力学比在模拟中人为保持刚性的骨架中的水分子动力学更慢。相比之下，预测Co-MOF-74中的水动力学因骨架振动而加速。这种不同行为的根源直接与水如何与这两种骨架相互作用有关，而这又决定了孔中不同的氢键模式。虽然吸附在[Zn(l-L)(Cl)]中的第一个水分子向Zn-Cl基团提供一个氢键，并将另一个氢原子指向孔的中心，但吸附在Co-MOF-74中的水分子最初通过其氧原子与骨架的钴原子结合，从而使每个分子能够与以更高负载量吸附的其他分子自由形成两个氢键。模拟结果表明，在计算机模拟中考虑骨架柔性对于金属有机骨架中吸附和传输过程的定量建模是必要的。
