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Spin Crossover and High-Spin State in Fe(II) Anionic Polymorphs Based on Tripodal Ligands
Emmelyne Cuza1, Cle Donacier Mekuimemba1, Nathalie Cosquer1
1Univ Brest, CNRS, CEMCA, 6 Avenue Le Gorgeu, C.S. 93837-29238 Brest Cedex 3, France.
Inorganic Chemistry
|April 12, 2021
Summary
Two new iron(II) polymorphs were synthesized, with one exhibiting a spin crossover (SCO) transition near 132 K and a photoinduced high-spin state. The other polymorph remained in a high-spin state across the studied temperatures.
Area of Science:
- Coordination Chemistry
- Materials Science
- Solid-State Physics
Background:
- Iron(II) complexes are known for exhibiting spin crossover (SCO) behavior, a phenomenon with potential applications in molecular switches and sensors.
- Polymorphism in coordination compounds can lead to distinct physical properties, including variations in magnetic behavior.
- Understanding the interplay between molecular structure and spin state in iron(II) complexes is crucial for designing functional materials.
Purpose of the Study:
- To synthesize and characterize novel mononuclear Fe(II) polymorphs with a tris(pyridin-2-yl)ethoxymethane ligand.
- To investigate the magnetic and photomagnetic properties of these new Fe(II) complexes.
- To elucidate the structural changes associated with spin crossover transitions and photoinduced spin states.
Main Methods:
- Single-crystal X-ray diffraction for structural determination at different temperatures.
- Variable-temperature magnetic susceptibility measurements to probe spin states.
- Variable-temperature infrared spectroscopy and photomagnetic measurements to study spin crossover and light-induced effects.
Main Results:
- Two new Fe(II) polymorphs, [(C2H5)4N]2[Fe(py3C-OEt)(NCS)3]2 (1) and [(C2H5)4N][Fe(py3C-OEt)(NCS)3] (2), were successfully synthesized and structurally characterized.
- Polymorph 2 maintained a high-spin (HS) state from 10 to 300 K, while polymorph 1 displayed an abrupt spin crossover (SCO) transition at approximately 132.3 K.
- Polymorph 1 also exhibited a metastable photoinduced HS state with a light-induced excited spin-state trapping (LIESST) temperature of 70 K, confirmed by photomagnetic and photoinfrared spectroscopy.
Conclusions:
- The synthesized Fe(II) complexes demonstrate distinct magnetic behaviors dependent on their polymorphic form.
- Complex 1 showcases a thermally and photoinduced spin crossover, highlighting its potential for bistable molecular devices.
- The structural modifications observed during the SCO transition in complex 1 correlate well with changes in Fe-N bond lengths and coordination sphere distortions.
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