Mechanically Interlocked Linkers for Dynamic Metal-Organic Frameworks
This dissertation has been directed at transferring the superb dynamics and machine-like properties observed for mechanically interlocked molecules (MIMs) in solution, into crystalline metal-organic frameworks (MOFs). Chapter 1 gives a brief introduction to MIMs and outlines all previous work towards incorporation of rotaxane linkers into metal-organic frameworks. Chapter 2 describes how a paradigm shift in the development of such systems resulted in a robust rotaxane linker that was used to create a novel material, UWDM-1 (University of Windsor Dynamic Material), which for the first time, exhibited dynamic motion related to the wheel component of a MIM inside a solid state material. Analysis via variable temperature 2H SSNMR proved that a dense array of soft [24]crown-6 macrocycles were able to rapidly rotate and sample multiple conformations while mechanically linked to the rigid metal-organic framework. In Chapter 3, a series of MIM linkers were synthesized utilizing the same anilinium-based axle with different sized macrocyclic rings, 22C6, 24C6, and B24C6. Ultimately, an isomorphous series of MIM in MOF materials was able to be created (UWDM-1(22), UWDM-1(24), and UWDM-1(B24)) in which the macrocyclic rings within each material exhibited different degrees of motion. In Chapter 4, a new MIM linker was developed and successfully implemented into robust MIM-pillared MOFs UWDM-2 and á UWDM-3. A reversible phase change in á UWDM-3 to â UWDM-3 demonstrated for the first time that the dynamic motion of a macrocyclic wheel component of a MIM inside a MOF can be controlled by an external perturbation; in this case via a reversible phase change of the material. In Chapter 5, a series of rigid benzo-bis-imidazolium based [2]rotaxane shuttles were synthesized. Acid base experiments indicated that the MIMs were also able to function as chemically stable colorimetric or fluorescent switches for future incorporation into metal-organic frameworks. In Chapter 6, mechanically interlocking a 24-membered macrocycle around a linker allows synthesis of a previously unattainable MOF, UWCM-2. Subsequent removal of the macrocycles by post-synthetic modification utilizing Grubbs-Hoveyda II catalyst generates a potentially high porosity MOF not accessible by any other synthetic protocol, other than Reversible Mechanical Protection (RMP).
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