Date of Award
Chemistry and Biochemistry
Dynamic Properties, MIM, MOF, Post-synthetic, rotaxane, Templating motif
This dissertation is focused on designing new recognition motifs to develop mechanically interlocked molecules (MIM) and transferring the dynamics properties of these MIMs into crystalline metal-organic frameworks (MOFs). Chapter 1 gives an introduction to rotaxanes, their application as molecular machines and their incorporation into MOFs. It also describes some recent success in creating rotaxane-based MOFs that show rotational and translational motion. Chapter 2 describes the design of a new templating motif for the formation of pseudorotaxanes in which rigid, Y-shaped axles with an imidazolium core and aromatic substituents at the 2-, 4- and 5-positions interact with crown-8 ether wheels (crown-8 and dibenzocrown-8). The Y-shape of the axle had a significant effect, raising the association between axle and wheel compared to those found for simple imidazolium or benzimidazolium derivatives. In chapter 3, the Y-shaped 2,4,5 triphenylimidazolium recognition site was combined with the T-shaped 2,4,7-triphenylbenzimidazolium site to develop a rigid bistable rotaxane molecular shuttle. Studies on the molecular shuttling in both the neutral and di-cationic states demonstrated the position of a 24-membered crown ether macrocycle can be controlled by acid-base chemistry. In chapter 4, a new MIM linker was developed by using ring-closing metathesis (Grubbs I) which allowed clipping of a crown 6 ether (24C6) wheel around an axle containing both Y-shaped di phenyl-imidazole and isophthalic acid groups. It was successfully incorporated into a Zn-based MOF, UWDM-5. VT 2H SSNMR studies showed that the macrocyclic ring of UWDM-5 undergoes rapid, thermally driven rotation about the axle inside the pores of the MOF at temperatures above 150 oC. In chapter 5, a new MIM linker was made by using ring-closing metathesis to clip a crown 6 ether (24C6) wheel around an axle containing bis(imidazolium) recognition site. A robust MOF material, UWDM-6, was constructed using this linker and Zr(IV) ions. VT 2H SSNMR Studies on the dynamic motion of the macrocyclic ring in the neutral, di-cationic and Li-doped version of UWDM-6 demonstrated the overall motion of the macrocycle inside the MOF is not significantly affected by protonation or Li+ chelation of the bis(imidazole). In Chapter 6, two Zr-based MOFs, UWCM-1 and UWCM-2 were synthesized using the bis(imidazole) rotaxane linker containing unreduced 24C6 wheel and naked bis(imidazole) linker, respectively. Subsequent ring removal of UWCM-1 by post-synthetic modification utilizing Hoveyda-Grubbs II catalyst generated a MOF with a different topology which is identical to UWCM-2. Indeed, ring removal of UWCM-1 leads to structural transformation of the MOF while the Zr clusters still remain intact.
Farahani, Nasim, "Interlocked Molecules and Materials with an Imidazole Core" (2016). Electronic Theses and Dissertations. 5819.