UC San Diego

Metal-organic frameworks (MOFs) are a relatively new class of porous materials comprising a metal structural node and an organic building unit. These materials are modular in nature, allowing for a wide variety of solids to be constructed. This flexibility brings with it the ability to tune the frameworks for a range of applications. Coordinatively unsaturated metal sites within the MOF have been observed to alter the frameworks interaction with guest molecules, and as such much work has been done to design solids with these open metal sites. Post synthetic modification (PSM) of the prefabricated solid is commonly carried out to alter the framework, giving new functionality. This method, while extremely effective, does not always bring about the desired function. By choosing organic building units that are already chemically active, new solids can be formed that do not require extensive PSM techniques to activate the solid. In Chapter 2, the novel solid constructed using tetrakis-(4- caboxyphenyl) porphyrin (TCPP) is presented. The solids 2- M (M = Fe, Co, Ni, Cu, Zn, Cd, Pd) are built of two- dimensional slabs and represent an isostructural series of frameworks. Using a one-pot synthesis technique, the metal ion coordinated to the porphyrin ring was altered. The solids were than shown to retain the same structure using powder X-ray diffraction and the identity of the metal bound to the porphyrin core was verified using UV-vis and atomic absorbance spectroscopy. The solid 2-M was probed for possible catalytic activity due to the reactive nature of Fe-porphyrin systems. Chapter 3 focuses on a second family of isostructural frameworks, again built from the organic building block TCPP. The family of frameworks 3-M (M = V, Mn, Fe, Co, Cu, Zn, Pd, Cd) have two-dimensional square grid structures. This series of solids is shown to have a large dependence on temperature with respect to the inter layer distance. The accessibility to the porphyrin metal centers is shown as the V, Mn, Fe and Co frameworks all catalyze the oxidation of alkanes and alkenes. Additionally the degradation of the bio-polymer lignin is observed. Chapter 4 describes the two-dimensional solid using manganese as the metal which defines both the structural site and the functional site. This solid, 4-Mn, is similar to 3-M, in that the framework is built from stacked two-dimensional sheets. The Mn-porphyrin unit is a known catalyst for oxidation of alkanes and alkenes, and as such, this frameworks activity towards small molecules is probed. Additionally the degradation of lignin is observed using this MOF. Chapter 5 describes in detail the synthesis of four distinct three-dimensional solids built using TCPP as the organic building unit. While these solids are not an isostructural series, they are closely related based on the coordination environment of the Cd(II) ions defining the structural node. The dependence on the ligand coordinated axial to the metal bound to the porphyrin is seen when the structural node is defined during the solvothermal process. Chapter 6 describes three structures that were discovered during the optimization of reactions for those found in the previous chapters. These solids, while be interesting of their own accord, were not pursued because bulk samples could not be prepared. Continued work on these solids is to be continued owing to the success of previous materials by future graduate students in the Beauvais lab