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Solvent-Induced Polymorphism of Iron(II) Spin Crossover Complexes.
Ivan Šalitroš1,2, Olaf Fuhr3,4, Mario Ruben5,6
1Institut für Nanotechnologie, Karlsruher Institut für Technologie, Postfach 3640, Karlsruhe 76021, Germany. ivan.salitros@stuba.sk.
Materials (Basel, Switzerland)
|August 5, 2017
Summary
Two new iron(II) compounds were synthesized, exhibiting distinct solvent forms and spin crossover behaviors. Desolvation altered spin transition temperatures and hysteresis, with one compound remaining locked in a high-spin state.
Area of Science:
- Coordination Chemistry
- Materials Science
- Solid-State Chemistry
Background:
- Iron(II) complexes are known for their spin crossover properties, crucial for molecular switches and sensors.
- Solvent molecules within crystal lattices can significantly influence the spin transition behavior of metal complexes.
Purpose of the Study:
- To synthesize and characterize novel mononuclear iron(II) compounds with potential spin crossover applications.
- To investigate the impact of solvent molecules and desolvation on the spin transition properties of iron(II) complexes.
Main Methods:
- Synthesis of iron(II) compounds with a 4-(2-bromoethyn-1-yl)-2,6-bis(pyrazol-1-yl)pyridine ligand.
- Single-crystal X-ray diffraction to determine crystal structures and solvent content.
- Magnetic susceptibility measurements to study spin crossover transitions.
- Variable-temperature studies to analyze the effects of desolvation on spin states.
Main Results:
- Two solvent analogues, [Fe(L)₂](BF₄)₂·CH₃CN (1) and [Fe(L)₂](BF₄)₂·2CH₃CN (2), were synthesized and structurally characterized.
- Both compounds exhibit low-spin (LS) states at 180 K and high-spin (HS) states at higher temperatures, confirmed by X-ray and magnetic studies.
- Spin transitions occurred at different temperatures for (1) and (2) (above 293 K and 237 K, respectively), influenced by solvent content.
- Desolvation of (1) resulted in a higher transition temperature (342 K) with hysteresis, while desolvated (2) remained in the HS state.
Conclusions:
- The synthesized iron(II) complexes demonstrate tunable spin crossover behavior influenced by solvent molecules.
- Desolvation significantly modifies the spin transition characteristics, enabling the design of materials with distinct thermal switching properties.
- Compound (1d) shows potential for bistable molecular switching due to its hysteresis loop after desolvation.
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