This work encompasses inorganic and physical chemistry to ask how halogenation of select ligand influences the spin-crossover properties of the Fe and Co complexes. Previous work has shown complexes with spin-crossover transitions at very low temperatures (~200K). This low temperature is not viable for any scalable storage method. There has been a reported complex using 2,6-di(pyrazol-1-yl)pyridine ligands complexed with iron with a transition temperature of 260K. Combining this knowledge with previous work illustrating changing temperatures for different halogen substituents allows for the ability to look at halogen type and metal center type for crossover temperature optimization. This would allow for the tunability of complexes in the quest to make quantum data-storage devices and switches commercially viable. The ligands were synthesized and complexed with the corresponding metal center. Hydrogen, and Fluorine-NMR were used for characterization and qualitative examinations of halogen effects on the structure. UV-Vis measurements probed the electronic transitions qualitatively. Both NMR and UV-Vis showed influences from the halogen depending on the metal complex, with bromine showing interesting shifts compared to iodine and chlorine. Qualitative differences were also seen between the cobalt and iron complexes due to their differing electronic structures. Fluorine NMR results showed counter anion-complex interaction, confirming previous work showing complex-anion interactions effecting crossover temperatures. Interestingly, the UV-Vis spectra showed only metal to ligand interactions when d to d transitions were expected to be seen as well. Quantitative measurements using NMR techniques and quantum mechanical models to obtain relaxation rates are ongoing to get a clearer picture. Future work will be to compare with the PF6 anion counterparts.
Author: Samuel Tyndall
Faculty Advisor: David Tierney, Chemistry and Biochemistry
Graduate Student Advisor: Nuwanthika Kumarage, Chemistry
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