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Updated: Dec 31, 2025
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Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals
Published on: April 14, 2020
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Spin crossover in mononuclear Fe(II) complexes based on a tetradentate ligand
Xin Yu1, Tian Yang Chen1, Yi Shan Ye1
1School of Chemical Engineering, Nanjing University of Science and Technology, 210094 Nanjing, People's Republic of China.
Summary
Three iron complexes exhibit spin crossover (SCO) activity, with high transition temperatures for iron(II)-cyanide derivatives. These complexes show strong ligand field effects but limited cooperativity due to supramolecular interactions.
Area of Science:
- Coordination Chemistry
- Materials Science
- Solid-State Chemistry
Background:
- Spin crossover (SCO) phenomena in iron(II) complexes are crucial for developing molecular switches and sensors.
- The ligand field (LF) strength and cooperativity significantly influence SCO properties, making ligand design paramount.
- Isostructural complexes offer a platform to systematically study structure-property relationships in SCO materials.
Purpose of the Study:
- To synthesize and characterize novel isostructural iron(II) complexes with varying NCE- co-ligands (E = S, Se, BH3).
- To investigate the spin crossover behavior, including transition temperatures and cooperativity, of the synthesized complexes.
- To elucidate the factors governing ligand field strength and cooperativity in these Fe(II)-NCE systems.
Main Methods:
- Single-crystal X-ray diffraction for structural determination.
- Magnetic susceptibility measurements to probe spin crossover transitions.
- Differential Scanning Calorimetry (DSC) studies for thermal analysis.
- UV-Vis spectroscopy on analogous Ni(II) complexes to assess ligand field strength.
Main Results:
- Three isostructural [Fe(L5Me)(NCE)2] complexes (E = S, Se, BH3) were successfully synthesized and characterized.
- All derivatives displayed active spin crossover with complete one-step spin conversion and high SCO midpoint temperatures (193 K, 226 K, 330 K).
- Strong N-H…E hydrogen bonding formed 2D supramolecular sheets, but insufficient for significant cooperativity transmission.
Conclusions:
- The NCE- co-ligands impose a strong ligand field, leading to high SCO transition temperatures.
- While supramolecular interactions are present, they do not sufficiently promote cooperativity in these systems.
- The study provides insights into tuning LF strength and cooperativity in Fe(II) SCO complexes.
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