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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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Light-induced spin-state switching in Fe(II) spin-crossover complexes with thiazole-based chelating ligands
Minyoung Jo1, Botagoz Amanyazova1,2, Sandugash Yergeshbayeva1
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA. shatruk@chem.fsu.edu.
Dalton Transactions (Cambridge, England : 2003)
|June 6, 2024
Summary
Iron(II) complexes with thiazole-based ligands exhibit tunable spin crossover behavior. Stronger intermolecular interactions promote cooperative spin transitions and light-induced excited spin state trapping (LIESST) in these materials.
Area of Science:
- Coordination Chemistry
- Materials Science
- Solid-State Physics
Background:
- Spin crossover (SCO) in iron(II) complexes is a phenomenon with potential applications in molecular switches and sensors.
- Thiazole-based ligands offer tunable electronic and steric properties for designing SCO materials.
- Understanding the influence of crystal packing and intermolecular interactions on SCO behavior is crucial for material design.
Purpose of the Study:
- To synthesize and characterize novel homoleptic iron(II) complexes with thiazole-based bidentate ligands.
- To investigate the spin crossover properties and crystal structures of these complexes.
- To explore the light-induced excited spin state trapping (LIESST) phenomenon and relaxation dynamics.
Main Methods:
- Synthesis of iron(II) complexes with 4,4'-bithiazole (4bt), 2,2'-bithiazole (2bt), and 3-(thiazol-2-yl)pyrazole (3tpH) ligands.
- X-ray crystal structure determination to analyze crystal packing and intermolecular interactions.
- Variable-temperature magnetic susceptibility measurements to study spin crossover transitions.
- Optical absorption spectroscopy to investigate LIESST and relaxation dynamics.
Main Results:
- Three homoleptic iron(II) complexes, [Fe(4bt)3](ClO4)2 (1), [Fe(2bt)3](ClO4)2 (2), and [Fe(3tpH)3](ClO4)2 (3), were successfully synthesized.
- Crystal structures revealed varying intermolecular interactions, with stronger interactions in 2·MeOH and 3·2(3tpH) complexes.
- Complexes 2 and 3·2(3tpH) exhibited cooperative spin transitions at 235 K and 159 K, respectively, and displayed LIESST behavior.
- Complex 1 showed gradual spin crossover above 300 K due to weaker interactions.
- Relaxation dynamics of the LIESST state in 3·2(3tpH) indicated cooperative effects and complex relaxation mechanisms.
Conclusions:
- The spin crossover behavior and LIESST properties of iron(II) complexes are strongly influenced by ligand choice and crystal packing.
- Cooperative effects, arising from specific intermolecular interactions, play a significant role in the SCO and relaxation dynamics.
- These findings provide insights into the rational design of molecular materials with switchable properties.
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