Date of Award

12-7-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Anindya Ghosh

Second Advisor

Patrick Desrochers

Abstract

Cobalt(II) scorpionates possess distinct electronic and magnetic properties in comparison to other first-row transition metal complexes in this ligand class. One unique property is their significantly downfield paramagnetically shifted 11B NMR signals. The utilization of a heteroscorpionate ligand Tp’ introduces asymmetry to metal scorpionates, producing cis and trans isomers. cis- and trans-Co(Tp’)2 were synthesized and separated by column chromatography. 11B NMR data show cobalt(II) homoscorpionates resonances in a narrow 20 ppm shift range around 270 ppm while cis- and trans-Co(Tp’)2 differ with signals at 230 ppm and 140 ppm, respectively. Paramagnetic NMR studies indicate both isomers maintain the same spin state in a 200K to 350K range, exhibit Curie-Weiss behavior, and that trans has a magnetic moment higher than traditional cobalt(II) homoscorpionates. EPR measurements and theoretical calculations of Co(Tp’)2 indicate trans-Co(Tp’)2 to be in a more rhombic electronic environment with a lower zero-field splitting value than cis-Co(Tp’)2 and both potentially possessing an Ms = 3/2 ground state. Reversible redox activity has been observed in both Co(Tp’)2 isomers via CV and 11B NMR, where the paramagnetic cobalt(II) peaks are replaced by the diamagnetic cobalt(III) peak. Inequivalent pyrazole methyl groups of Tp’ are revealed in cis-[Co(Tp’)2+] versus the equivalent methyl groups in¬ trans-[Co(Tp’)2+]. This fundamental understanding of cobalt(II) and cobalt(III) in various scorpionate ligand environments should allow for the fine tuning of magnetic properties in scaffolded molecular magnets in nano-scale devices and candidates for thermometry applications.

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