溶剂化效应对金属-有机骨架材料界面微环境催化性能的影响

金属-有机骨架材料（metal-organic frameworks，MOFs）的纳微结构可根据特定需求进行功能化调控，有望成为良好的工业催化材料。由于溶剂环境可对其界面微环境及催化性能产生较大影响，因此研究溶剂化效应对于MOF材料的影响具有重要的意义。以Cu-BTC和MOP-15两种典型MOF材料作为研究对象，采用密度泛函理论与COSMO溶剂模型相结合的方法，考察了溶剂效应对材料几何结构与电子稳定性的影响，并研究了不同溶剂对其Lewis酸性的影响。结果表明，溶剂环境可以使材料中的电子从不饱和配位金属处转移到有机配体上，进而使材料具有更强的Lewis酸性，并且电负性较大有机配体构成的MOF材料，受溶剂效应的影响更加显著。本工作将有助于深入理解溶剂化对调控MOF材料液相催化活性的影响。

Solvent effect on catalytic properties of microstructures in metal-organic frameworks

The nanoporous structures of metal-organic frameworks (MOFs) can be functionally regulated according to specific targets of interest, and thus such types of solids can be considered as promising industrial catalytic materials. Since interface microenvironments and catalytic properties of MOFs might be affected by the solvents, it is necessary to study the influence of solvent effects on their catalytic activities. Although MOFs with coordinatively unsaturated metal sites (CUMs) have shown promising applications in liquid-phase catalysis, the related solvent effects on the Lewis acid catalytic performance of these CUMs are seldom investigated. In this work, density functional theory calculations were conducted to investigate the solvent effects on the properties of the Lewis acid sites in two typical MOFs, Cu-BTC and MOP-15, where the COSMO (conductor-like solvent model) was used to mimic the dielectric response of the solvent environments. Different relative dielectric constants were considered, including in vacuum, toluene, ethyl acetate, 1, 2-dichloroethane and acetonitrile. Using CO as the probe molecule, the solvent effects were examined by exploring the geometry parameters, the Mulliken charges, and the vibrational frequency as well as the adsorption energy of CO molecule around those CUMs. The strengths of Lewis acid sites could be enhanced with the increase of the dielectric constant. Further, the solvent effects became more evident in CUMs when the organic linkers had higher electronegativity. These observations provide fundamental insights into the regulation of the liquid-phase catalytic activity of MOFs using specific solvents.