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Chemically Separable Co(II) Spin-State Isomers.
Amelia M Wheaton1, Jill A Chipman1, Rebecca K Walde1
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, United States.
Journal of the American Chemical Society
|September 19, 2024
Summary
Researchers report the first physically separable cobalt(II) spin-state isomers. These distinct isomers, arising from a Mo-Co complex, can be isolated due to differences in solubility and interconversion rates.
Area of Science:
- Coordination Chemistry
- Materials Science
- Spectroscopy
Background:
- Spin crossover (SCO) complexes exhibit switchable spin states and geometric changes.
- SCO isomers typically interconvert rapidly and are difficult to separate due to similar polarity.
Purpose of the Study:
- To report the first example of physically separable cobalt(II) spin-state isomers.
- To characterize these isomers and understand the factors enabling their separation.
Main Methods:
- Synthesis of heterometallic Mo-Co compounds.
- SQUID magnetometry and EPR spectroscopy for spin state determination.
- X-ray crystallography to analyze geometric differences.
- Solubility studies and NMR, EPR, UV-vis spectroscopy for solution behavior.
Main Results:
- Successfully synthesized and isolated two distinct cobalt(II) spin-state isomers (SC-2 and HS-2) with identical composition (Mo2Co(dpa)4Br2).
- SC-2 exhibits an S=1/2 to S=3/2 spin transition, while HS-2 has a ground state of S=3/2.
- Geometric differences, specifically Co-Br bond length, and resulting solubility variations enabled physical separation.
- Isomers interconvert slowly in solution, with solvent polarity influencing the predominant form.
Conclusions:
- Demonstrated the first physical separation of cobalt(II) spin-state isomers.
- Highlighted the role of geometric and solubility differences in isomer separation.
- Showcased solvent-dependent isomer populations, offering new avenues for controlling SCO behavior.
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