Synthesis and Characterization of Redox-Active Metal–Organic Frameworks
This dissertation documents efforts to use a variety of synthetic approaches to generate new redox-active metal–organic frameworks and improve the properties of known frameworks. Chapter 1 introduces the field of metal–organic frameworks and discusses observed redox activity of metal nodes and organic linkers. Additionally, the application of the Langmuir-Freundlich gas adsorption model and the use of IAST selectivity calculations to quantify and predict gas sorption in metal–organic frameworks are discussed. Chapter 2 discusses the successful targeted synthesis of the templated, mixed-metal framework Fe–Zn(dobdc) with proposed short-range order in the metal distribution. This ordered system demonstrates thermal stability for O2 adsorption compared to both monometallic Fe2(dobdc) and nontemplated Fe~Zn(dobdc) via a suite of in situ techniques. Chapter 3 documents the first isolation of the highly oxygen-sensitive framework FeII(H2gallate)∙2H2O. This unusual material exhibits remarkable permanence of crystallinity upon exposure to air as shown by single-crystal-to-single-crystal diffraction experiments. Isothermal gas adsorption measurements reveal an unparalleled selectivity for ethylene over ethane stemming from size exclusivity in narrow framework pores. The redox activity of this system is leveraged to tune gas sorption properties in a mixed-valent isomer: FeII/III(Hxgallate). Chapter 4 details efforts to apply several different solvent-free synthetic approaches to the synthesis of both iron- and early transition metal-containing frameworks. Melt based reactions are used to obtain a layered two-dimensional solid, Fe(bzimid)2, as well as the crystalline metallocene-derived materials Cr–bzimid and V–bzimid. A high-temperature metal-powder-based synthetic route is successfully applied for the first time for an iron-based metal–organic framework in the case of Fe(imid)2. Additionally, air- and solvent-free ball milling is shown to increase reaction yields for metal–gallate frameworks and provide evidence of redox activity in the gallate linker. Lastly, Appendix A details the design and use of the Breen adapter, a glass tube adapter with important uses in the field of metal–organic frameworks.