Redox-coupled spin crossover in cobalt coordination complexes

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Authors
McCabe, Charles
Issue Date
2024-05
Type
Electronic thesis
Thesis
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en_US
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Chemistry
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Abstract
Cobalt coordination compounds consisting of a single five-coordinate cobalt(III) salen (CoIIISln+) complex and two cobalt β-diketonate complex [(Co(acac)2((CC)2bpy)] and [Co(dbm)2((CC)2bpy)] were synthesized. The redox-coupled spin crossover behavior of these complexes were then studied using electrochemical and spectroscopic methods. CoIIISln+ is high-spin in both its +2 and +3 oxidation states, but its remaining open coordination site allows for exogenous ligands to bind to the +3 oxidation state inducing a high-spin to low-spin transition. This transition is accompanied by changes in color and induces a drastic electrochemical shift. The changes in electrochemistry correlate nicely to the basicity of the ligand as measured by gas phase basicity. For pyridine ligands the shift also correlates to the Hammett parameter of the para substituent. This complex is a notable example of a cobalt complex which undergoes both redox-coupled spin crossover and coordination-induced spin crossover. In pursuit of a better understanding of these interactions a review of similar coordination-induced spin crossover systems was performed. The two β-diketonates also undergo redox-coupled spin crossover. The +2 oxidation states are both high-spin, but upon oxidation a rearrangement takes place that results in a low-spin cobalt(III) metal center. Like CoIIISln+, the high- and low-spin states of [Co(acac)2((CC)2bpy)] and [Co(dbm)2((CC)2bpy)] have very different spectral properties. Attempts to fashion electrochromic multilayers out of these complexes were unsuccessful. These failed experiments provided insights into the synthetic modifications needed for related complexes to be made into functional multilayers and multiple future directions for this research is discussed.
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May2024
School of Science
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Rensselaer Polytechnic Institute, Troy, NY
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