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Unprecedented bistability domain and interplay between spin crossover and polymorphism in a mononuclear iron(II)
Mark B Bushuev1, Vasiliy A Daletsky, Denis P Pishchur
1Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com.
Dalton Transactions (Cambridge, England : 2003)
|January 22, 2014
Summary
This study explores spin crossover in an iron complex, [FeL2](BF4)2·xH2O, demonstrating its conversion into multiple phases with distinct spin states. Different heating and cooling protocols yield various high-spin and low-spin phases, showcasing complex spin crossover behaviors.
Area of Science:
- Coordination Chemistry
- Materials Science
- Supramolecular Chemistry
Background:
- Spin crossover (SCO) materials are molecular switches responding to external stimuli.
- Iron(II) complexes are widely studied for their SCO properties.
- Understanding phase transitions in SCO complexes is crucial for device applications.
Purpose of the Study:
- To investigate the spin crossover behavior of a mononuclear iron(II) complex, [FeL2](BF4)2·xH2O.
- To characterize the different spin states (high-spin and low-spin) and phase transitions induced by thermal stimuli.
- To explore the influence of dehydration and annealing on the SCO properties.
Main Methods:
- Synthesis and characterization of the mononuclear iron(II) complex [FeL2](BF4)2·xH2O.
- Thermal analysis (heating and cooling cycles) to induce and monitor spin transitions.
- Investigation of dehydration effects at different temperatures.
- Characterization of resulting phases and their spin crossover properties.
Main Results:
- The hydrated complex (1LS∙xH2O) dehydrates to form high-spin phases (1A/HS, 1C/HS) and subsequently a low-spin phase (1A/LS).
- A wide hysteresis loop (130 K) is observed for the 1A/LS↔1A/HS transition.
- Annealing yields 1C/HS, which converts to 1C/LS (T1/2 ≈ 320 K).
- Dehydration at specific temperatures produces 1X/LS, which transforms irreversibly to 1B/HS and then reversibly to 1B/LS (T1/2 ≈ 320 K).
Conclusions:
- The iron(II) complex exhibits rich spin crossover behavior, forming multiple distinct phases.
- Thermal treatment, including dehydration and annealing, significantly influences the SCO properties and phase formation.
- The observed hysteresis and phase interconversions highlight the potential for complex molecular switching functionalities.
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