UC Berkeley

The work presented here focuses on expanding the chemistry of multivariate metal-organic frameworks (MTV-MOFs) by incorporating new linkers into existing MOFs while optimizing the composition for a target application. MTV systems create very complex pore environments, with many linker combinations possible within any MTV-MOF crystal. MTV-MOFs can enhance the performance of MOFs in a variety of fields but identifying the correct linker functionalities and their respective incorporations remains crucial to optimizing that performance. Chapter 1 provides a general introduction to MTV-MOFs, highlighting the history of their development and how linker distributions are characterized. The generation of heterogeneity in MOFs is also explained and correlated with the different types of heterogeneity that can be introduced. Introducing heterogeneity by post-synthetic exchange (PSE) after MOF synthesis is explained with selected studies highlighting the power of this approach. Finally, the structural details of the MOFs used in the subsequent chapters are explained to provide a reference for in-formation about those MOFs. Chapter 2 describes the study of MTV-MOF-5 containing 36 different linkers, which in-corporate 27 unique functionalities to the resulting crystals. The functionalities present on the linkers include amine, nitro, halide, naphthalene, alkyne, alkene, alkane, ether, phenyl, pyridine, thiophene, and amide groups. Each linker was found to make up between 0.07 and 6.64% of the linkers in the structure, with the total framework mass consisting of 74.8 to 75.1% linker molecules, compared to 63.9% for the linkers in MOF-5. 34 of the 36 linkers had linear correlations between the starting ratio and final incorporation, indicating interactions between linkers do not heavily influence the incorporation of other linkers into the final structure despite a record number of linkers being incorporated to a single MOF. Chapter 3 uses post-synthetic exchange (PSE) to modify the linkers in UiO-67 based on a guest molecule template. The linkers that are incorporated with different guests are analyzed along with how the final MOF composition affects competitive uptake of those guests. The roles of the solvents used for exchange and washing are explored, and how each unique functional group behaves during PSE and guest uptake. Chapter 4 uses linkers functionalized with crown ether groups to make MTV-MIL-53, UiO-66, and UiO-67 for cation separation. The size of the crown ether rings compared to the metal ion adsorbed and the crystallinity of each MOF are considered in analyzing how ion uptake varies between each MTV-MOF. The crown ether composition is controlled to generate MTV-MOFs with a desired final composition of crown ether functionalized MOFs. Chapter 5 serves as a conclusion to the various uses of MTV-MOFs studied and the effects of functionalities on their properties. This chapter also provides an outlook for future experiments in these fields and for MTV-MOFs in general.