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Rational Design of Iron Spin-Crossover Complexes Using Heteroscorpionate Chelates.
Patrick J Desrochers1, Ali Abdulrahim1, Katherine R Demaree1
1Department of Chemistry and Biochemistry, University of Central Arkansas, Conway, Arkansas72035, United States.
Inorganic Chemistry
|November 15, 2022
Summary
This study details iron(II,III) sandwich complexes, Fe(Tp')₂, revealing their spin crossover (SCO) behavior. These complexes exhibit significant differences in SCO between solution and solid states, with potential applications in molecular switches.
Area of Science:
- Coordination Chemistry
- Materials Science
- Magnetochemistry
Background:
- Iron(II,III) sandwich complexes (Fe(Tp étaire)₂) exhibit tunable optical, structural, and magnetic properties.
- Spin crossover (SCO) phenomena in iron complexes are crucial for developing molecular switches and sensors.
- The bis(3,5-dimethylpyrazolyl)benzotriazolylborate (Tp étaire) ligand offers unique steric and electronic properties.
Purpose of the Study:
- To investigate the optical, structural, and magnetic properties of Fe(Tp étaire)₂ complexes.
- To characterize the solution-phase and solid-state spin crossover (SCO) behavior of Fe(Tp étaire)₂.
- To explore the potential applications of these complexes in nanoscale magnetic devices.
Main Methods:
- Synthesis and crystallographic analysis of Fe(Tp étaire)₂ isomers (cis and trans).
- Paramagnetic ¹¹B NMR spectroscopy to study solution-phase SCO.
- Thermochemical measurements (solution and solid-state) to determine SCO parameters.
- Density Functional Theory (DFT) calculations to validate experimental findings and understand electronic properties.
- Magnetic measurements to investigate SCO hysteresis and thermal stability.
Main Results:
- Fe(II)(Tp étaire)₂ (orange) and Fe(III)(Tp étaire)₂⁺ (purple) complexes show strong MLCT bands.
- Crystallographic analysis confirmed geometric isomerism in chiral cis-Fe(Tp étaire)₂.
- Solution-phase SCO was observed for Fe(Tp étaire)₂, with endothermic LS to HS conversion and entropic preference for the HS state.
- Solid-state SCO in cis-Fe(Tp étaire)₂ exhibited thermal stability up to 520 K and magnetic hysteresis over 45 K.
- A significant difference in SCO transition temperatures (ΔTc ≈ 115 K) was observed between solution and solid states for cis-Fe(Tp étaire)₂.
- DFT calculations elucidated the role of benzotriazole rings in structural and optical properties.
- An adduct with tin(II) chloride ([cis-Fe(Tp étaire)₂-SnCl₂]) was characterized, showing no alteration of the iron(II) spin state.
Conclusions:
- Fe(Tp étaire)₂ complexes display distinct solution and solid-state SCO behaviors, with high transition temperatures in the solid state.
- The observed large solution/solid ΔTc is attributed to intermolecular interactions in the solid state.
- The Tp étaire ligand imparts functionality for potential integration into spintronic devices and nanoscale magnetic switches.
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