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Lattice solvent- and substituent-dependent spin-crossover in isomeric iron(II) complexes
Senthil Kumar Kuppusamy1, Asato Mizuno2, Lea Kämmerer3
1Institute of Quantum Materials and Technologies (IQMT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. senthil.kuppusamy2@kit.edu.
Dalton Transactions (Cambridge, England : 2003)
|June 3, 2024
Summary
Spin-state switching in iron(II) complexes is influenced by ligand substituents. Ethyl 2,6-bis(1H-pyrazol-1-yl)isonicotinate ligands enable bi-stable switching, while others trap high-spin states or show gradual transitions.
Area of Science:
- Coordination Chemistry
- Materials Science
- Solid-State Chemistry
Background:
- Spin-state switching (SCO) in iron(II) complexes is crucial for molecular switches.
- Ligand design significantly impacts SCO properties, including hysteresis and cooperativity.
- Understanding substituent effects is key to tuning SCO behavior in mononuclear iron(II) complexes.
Purpose of the Study:
- To investigate the influence of substituents on SCO in isomeric iron(II) complexes.
- To compare SCO behavior in complexes with ethyl 2,6-bis(1H-pyrazol-1-yl)isonicotinate (L1) and (2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)methylacetate (L2) ligands.
- To explore the relationship between molecular structure, SCO, and potential applications in molecular devices.
Main Methods:
- Synthesis of iron(II) complexes with BPP-based ligands (L1 and L2).
- Characterization of spin-state switching using temperature-dependent magnetic susceptibility measurements.
- Structural analysis of low-spin and high-spin forms to understand SCO mechanisms.
- Investigation of light-induced spin-state switching (LIESST effect).
Main Results:
- Complex 1·CH3CN (L1 ligand) exhibits bi-stable SCO with a wide hysteresis (44 K) and room-temperature switching (298 K).
- Complex 2a (L2 ligand) remains in the high-spin state, while complex 2b·CH3CN-Y shows gradual, non-hysteretic SCO.
- Both complexes 1·CH3CN and 2b·CH3CN-Y demonstrate light-induced spin-state switching at 5 K via LIESST.
- Structural analysis reveals pronounced distortion of the trans-N{pyridyl}-Fe-N{pyridyl} angle in the low-spin form of complex 1·CH3CN, correlating with hysteretic SCO.
Conclusions:
- Ligand substituents critically control spin-state switching behavior in iron(II) complexes.
- The observed bi-stable SCO in complex 1·CH3CN at room temperature highlights its potential for molecular switch applications.
- Structural distortions play a significant role in enabling hysteretic spin-state switching in the solid state.
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