Carboxylate-functionalized triphenylamine-based complexes : from discrete monomeric complexes to 2D and 3D extended frameworks
The goal of this thesis is the variable functionalization of the redox-active triphenylamine molecule with carboxylate groups which is expected to lead to varying possibilities from monocarboxylates (which can be used to generate simple complexes) to tricarboxylates (which have potential in producing coordination polymers). Varying the substituents on the para-positions of the monocarboxyltriphenylamine ligands and then merging with Cu(II) ions results in discrete complexes bearing the well-known paddle wheel motif. However, while the nature of the p-substituents had no effect on the magnetic behaviour of the Cu(II) units in the complexes, their electrochemical properties showed strong dependency on the electronic nature of these substituents. In the case of the trifunctionalized ligand, it was possible to obtain extended 2D and 3D networks with Co(II) ions. Simply combining the ligand with Co(II) ions in DMF yielded two different anionic networks depending on the geometry of the pressure reactor utilized for the synthesis. Furthermore, adding terephthalic acid as second ligand led to the formation of a third anionic pillared-layer framework with cage-like cavities. The bulky dimethylammonium counterion in the networks formed from the decomposition of DMF were easily replaced using smaller inorganic cations leading to increased access to the pores as well as higher surface areas. Using isophthalic acid instead of terephthalic acid resulted in a neutral fourth network composed of carboxylate-bridged trinuclear clusters. The isophthalic acid is believed to have played only a templating role in the formation of the eventual framework. Overall, the main thrust of this thesis is the remarkable flexibility of the tricarboxytriphenylamine ligand, by which a simple variation of the conditions and precursors yields different results. Additionally, the stability of the charged frameworks offers a possibility to tune the porosity of the ensuing structures via simple guest-ion exchange.