Porous Molecular Crystals and Metal-Organic Frameworks Based on Fluorinated Pyrazoles

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Non-technical abstractPorous materials have microscopic voids in their structures. Because these voids are comparable in dimensions to molecules, porous materials find numerous applications related to energy, petrochemical industry, environment, and medicine. With the support of the Solid State and Materials Chemistry program in the Division of Materials Research, this project develops new classes of porous materials in which building blocks are individual molecules. Such materials have superior properties relative to the currently available porous materials: they are lightweight, recyclable, and much more easily processable, as they are soluble and can in principle be "painted" on a surface. Their unusual internal structures make these materials superb water-repellants; they are also capable of capturing Freons and fluorocarbons-which are both powerful greenhouse gases and ozone-depleting substances. In addition, they strongly bind hydrocarbons, which makes them promising in applications in fuel storage and oil spill cleanup. This research project is integrated with a broad education plan that aims to increase student competency in the areas of energy and sustainability, as well as to involve undergraduate and high school students in original research, with a focus on minority and female students.Technical abstractThis collaborative project is focused on the preparation of extensively fluorinated porous materials based on pyrazoles. Fluorinated metal-organic frameworks are formed by deprotonation of pyrazoles into pyrazolates and their coordination to transition metals. Fluorinated pyrazolates have been chosen as ligands since their high basicity should translate into chemically robust frameworks. Fluorinated molecular crystals are formed by the self-assembly of neutral fluorinated pyrazoles into a porous framework held together by a combination of [pi···pi] stacking and hydrogen bonding. These porous molecular crystals were recently discovered by the principal investigators. This research fills a gap in the existing knowledge: extensively fluorinated porous materials have been underexplored because of the paucity of the appropriately fluorinated molecular precursors. This project will dramatically expand the knowledge in this area, through its four goals: (1) creation of a general synthetic strategy to access extensively fluorinated aromatic pyrazoles (and derivatives) through novel copper- and palladium-catalyzed C-H functionalization reactions; (2) reticulation of fluorinated pyrazoles into porous molecular crystals, and understanding of structural elements necessary for the creation of robust porosity that persists above 200 °C; (3) synthesis of extensively fluorinated metal-organic frameworks starting from the precursor pyrazolate ligands prepared in the first part of the proposed work, and (4) exhaustive characterization of both classes of fluorinated materials, with an eye toward future applications. Performance characteristics of interest include: thermal and chemical stability, hydrophobicity, and potential as adsorbents for (a) Freons and fluorocarbons, (b) fluorinated anesthetics, (c) amphiphilic fluorinated pollutants, (d) hydrocarbons, and (e) molecular oxygen. This research generates fundamental new knowledge in the areas of organometallic, inorganic, and supramolecular chemistry.