Tuning the Properties of Metal-Ligand Complexes to Modify the Properties of Supramolecular Materials
Date of Award
Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Ryan C. Hayward
E. Bryan Coughlin
Engineering | Materials Science and Engineering | Polymer and Organic Materials
Supramolecular chemistry is the study of discreet molecules assembled into more complex structures though non-covalent interactions such as host-guest effects, pi-pi stacking, electrostatic effects, hydrogen bonding, and metal-ligand interactions. Using these interactions, complex hierarchical assembles can be created from relatively simple precursors.
Of the supramolecular interactions listed above, metal-ligand interactions are of particular interest due to the wide possible properties which they present. Factors such as the denticity, polarizability, steric hindrance, ligand structure, and the metal used (among others) contribute to a dramatic range in the physical properties of the metal-ligand complexes. Particularly affected by these factors are the kinetic and thermodynamic properties of the complexes. As a result metal-ligand interactions can vary from inert to extremely transient.
Of the vast number of ligands available for study, this dissertation will center on substituted terpyridine ligands, with a particular focus on terpyridine-functionalized polymers. While polymer-functionalized terpyridine ligands and their complexes with transition metals have been heavily studied, the physical properties, particularly the effects of polymer functionalization on the stability of bis complexes of terpyridines, remain unexplored.
In the course of investigating the kinetic stability of these complexes, polymer functionalization techniques were developed which were found to increase the stability of the metal-ligand interactions compared to conventional techniques. In addition to studying the effect of terpyridine substituents, the effects of solvent on the stability of the complexes was studied as well. As polymer-bound terpyridine complexes are often studied in solvents other than water, knowledge of the stability of the complexes in organic solvents is important to create supramolecular structures with more precisely controlled properties. It was found that, for unsubstituted terpyridyl complexes, the stability of the complexes varied by as many as five orders of magnitude in common solvents. It is believed that this decrease in stability is the result of the ability of the solvent to facilitate the movement of the ligands from the first and second coordination spheres.
Although a large part of this dissertation is dedicated to the study of the kinetic stability of terpyridine complexes, synthetic techniques involving terpyridine and its complexes were investigated as well. It was found that terpyridine functionalized polystyrene could be produced by direction functionalization of terpyridine with polystyryllithium. Additionally heterloleptic terpyridine-based iron complexes were produced with high purity by reduction of the mono terpyridine complex of iron(III) in the presence of a second, functionalized terpyridine ligand. The culmination of these studies was the synthesis of supramolecular organogels, which were crosslinked using metal-terpyridine complexes, yielding dynamic mechanical properties could be broadly tuned by varying the metal used to form the crosslinks.
Henderson, Ian, "Tuning the Properties of Metal-Ligand Complexes to Modify the Properties of Supramolecular Materials" (2012). Open Access Dissertations. 555.