Computationally Driven Characterization of Magnetism, Adsorption, and Reactivity in Metal-Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) are a class of nanoporous materials that are composed of metal-containing nodes connected by organic linkers. The study of MOFs has grown in importance due to the wide range of possible node and linker combinations, which allow tailoring towards specific applications. This work demonstrates that theory can complement experiment in a way that advances the chemical understanding of MOFs. This thesis contains the results of several investigations on three different areas of MOF research: 1) magnetism, 2) CO2 adsorption, and 3) catalysis. The calculation of magnetic properties within MOFs is quite problematic due to the weak nature of the interactions between the metal centers. The metal atoms in MOFs can be far apart due to the organic linkers and are often in unique chemical environments that are diffcult to characterize. These weak interactions mean that the computational methods must be carefully selected and tested to attain adequate precision. The objective of the work in this thesis was to determine the single-ion anisotropy and magnetic ordering of Fe-MOF-74 before and after oxidation. MOFs have desirable properties for CO2 adsorption such as large pores and high surface areas. Accurate force fields are required in order to make predictions for adsorption interactions with the internal surface of MOFs. Therefore it is important to have computational protocols that enable the derivation of reliable interaction parameters in order to study the trends of adsorption for different metal centers. In the research herein we used ab initio calculations to compute parameters for classical force fields for members of the IRMOF-10 and the MOF-74 series. MOFs have been considered for catalysis due to their thermal stability, reactive metal sites, and large diameter pores. In this thesis we report a series of studies that advance the understanding of the reactivity of MOFs containing Zr6 and Hf6 polyoxometalate nodes. In the first study the proton topology of the nodes within NU-1000 was determined. Several other studies that make use of these MOFs as supports for single-site metal catalysts are also reported. Finally, research where NU-1000 serves as a template for a thermally stable nanocasted material used for high temperature Lewis acid catalysis is also discussed.