Date of Award

2016

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

First Advisor

Loeb, Stephen

Keywords

Dynamic Properties, MIM, MOF, Post-synthetic, rotaxane, Templating motif

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Abstract

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 [2]rotaxane-based MOFs that show rotational and translational motion. Chapter 2 describes the design of a new templating motif for the formation of [2]pseudorotaxanes in which rigid, Y-shaped axles with an imidazolium core and aromatic substituents at the 2-, 4- and 5-positions interact with [24]crown-8 ether wheels ([24]crown-8 and dibenzo[24]crown-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 [2]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 [24]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 [24]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) [2]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.

Share

COinS