UC Riverside

Supramolecular self-assembled metal-ligand cages have been used as reaction containers, molecular switches, and sensors. While many diamagnetic cage complexes are known, studies into spin-state switching cage complexes have only recently begun to emerge. These magnetically active complexes have applications in information storage, electronic switches, and display devices. To create stable, robust high spin complexes, new ligand structures must be explored focusing on the chelating portion of the ligand to affect the spin state of the metal centers.

This work analyzes the characteristics needed in ligands to form favorable paramagnetic cage complexes, using reversible multicomponent metal-ligand self-assembly methods. Using novel termini to interact as metal coordinators allows the formation of high spin Fe(II) metal centers. High spin Fe(II) can be obtained via two types of ligand interactions, either distortion of the octahedral coordination environment due to excess bulk at the metal center, or using a weak coordinator. The addition of steric bulk near the metal center requires a certain amount of flexibility in the ligand backbone to allow favorable coordination. The spin states of these paramagnetic systems were examined to determine their magnetic moments and define the relationship between the metal centers. Alternatively, spin state switching complexes can be formed by using novel heterocyclic chelators. Using new termini allowed creation of novel paramagnetic cages and subsequently the functional properties of these cages were investigated. Slight differences made it possible to tease out the relative favorability between the two seemingly energetically equivalent coordination positions of imidazole termini. Synthesis of novel ligands with amine termini was pursued to bestow a wider range of functionality on cage systems. New amine capped complexes were characterized and found to bind biological molecules of interest. Additionally, the amine-capped complexes were found to be much more sensitive to the counterion employed, distinctly limiting the number of isomers formed.