Through the Looking Glass: Exploration of the Synthesis and Design of Glass-Forming Metal Complexes

Abstract

Molecular glasses are a novel class of chemical compounds that have gained an increasing amount of attention in the development of functionalized thin film materials. The small size, low molecular weight, and monodisperse nature of these compounds lead to easier purification and characterization compared to traditional materials. Our research group has designed a class of compounds based on a mexylaminotriazine core that can readily adopt glassy phases and incorporate glass-forming properties into other molecular functionalities. The development of molecular glass coordination complexes could be used to form amorphous thin films for solid-state applications such as opto-electronics and heterogeneous catalysis. The goal of this research thesis is to develop a viable strategy for incorporating glass-forming properties into coordination complexes. Herein, the synthesis of a number of mexylaminotriazine-functionalized ligands and the subsequent preparation and characterization of a variety of corresponding coordination complexes is presented. Glass-forming salen derivatives incorporating mexylaminotriazine glass-forming moieties were synthesized. Symmetric and asymmetric glass-forming salen ligands were synthesized with ethylene and cyclohexane backbones, while, a mono-functionalized version was synthesized with a phenylene backbone. A number of first-row transition metal complexes were prepared from the asymmetric ligands and incorporate Mn(III), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) metal centres. Differential scanning calorimetry (DSC) demonstrated the glass-forming properties of most complexes, with the Co(II) complex being the only complex without a clear glass transition. As expected, the glass transition temperatures (Tg) of the coordination complexes were found to be higher than that of their respective ligands. The proposed cause is the loss of molecular mobility associated with the coordination of metal centres to these ligand structures. In addition, Tg values varied between metal complexes incorporating analogous ligands. An acetylacetone ligand incorporating a mexylaminotriazine substituent was also successfully synthesized. DSC was used to demonstrate the glass-forming properties and determine the Tg of this ligand. Attempts to prepare a variety of homoleptic and heteroleptic transition metal complexes with Zn(II), Ni(II), and Cu(II) metal centres were unsuccessful. Subsequent experiments suggest that the ligand was too labile, resulting in hydrolysis during the purification of the coordination complexes. Lastly, a mexylaminotriazine-functionalized phenanthroline ligand was synthesized. This ligand was subsequently used to prepare a number of heteroleptic lanthanide complexes from lanthanide(III) metal salts and two different β-diketones. The ligand and all corresponding complexes demonstrated glass transition temperatures and glass-forming properties via DSC. A lower Tg was observed amongst the resulting coordination complexes. The loss of hydrogen bonding interactions formed from the heteroaromatic nitrogen atoms of the phenanthroline moiety are the proposed cause. The Tg values were consistent amongst most complexes; however, the lanthanum(III) complexes in both series demonstrated higher Tg values. The optical properties of these complexes were found to be consistent with crystalline analogues. Furthermore, the two europium(III) complexes were observed to luminesce when irradiated by UV light. Similar properties have been reported in non-glass forming europium(III) complexes. This project has demonstrated that a library of mexylaminotriazine-functionalized ligands and their respective homoleptic and heteroleptic coordination complexes can be synthesized to incorporate novel glass-forming properties while maintaining the properties of their non-glassy analogues.