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Two-Step Spin Conversion for the Three-Dimensional Compound Tris(4,4'-bis-1,2,4-triazole)iron(II) Diperchlorate
Yann Garcia1, Olivier Kahn, Louis Rabardel
1Laboratoire des Sciences Moléculaires, Institut de Chimie de la Matière Condensée de Bordeaux, UPR CNRS No. 9048, 33608 Pessac, France, and Laboratoire de Chimie de Coordination, UPR CNRS No. 8241, 31077 Toulouse, France.
Inorganic Chemistry
|October 24, 2001
Summary
This study reveals a two-step spin conversion in a novel iron compound, [Fe(btr)(3)](ClO(4))(2). The conversion occurs across two distinct iron(II) sites, influencing magnetic properties and crystal structure.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Magnetochemistry
Background:
- Spin crossover (SCO) compounds containing iron(II) are of interest for molecular switches and memory devices.
- Understanding the factors governing SCO behavior, such as ligand environment and crystal packing, is crucial for material design.
Purpose of the Study:
- To synthesize and characterize the novel iron(II) complex [Fe(btr)(3)](ClO(4))(2).
- To investigate the spin conversion properties and structural changes associated with temperature variations.
- To elucidate the mechanism of the observed two-step spin conversion.
Main Methods:
- Synthesis of [Fe(btr)(3)](ClO(4))(2).
- Magnetic property measurements to detect spin transitions.
- Differential scanning calorimetry (DSC) to confirm phase transitions and quantify thermodynamic parameters.
- X-ray crystallography at variable temperatures (260 K, 190 K, 150 K) to determine structural changes.
- Mössbauer spectroscopy to monitor the spin state of iron ions.
Main Results:
- [Fe(btr)(3)](ClO(4))(2) exhibits a two-step spin conversion: a gradual high-temperature step (T(2) = 222 K) and an abrupt low-temperature step with hysteresis (T(1) = 184 K).
- Crystallographic analysis reveals two distinct Fe(II) sites (Fe1 and Fe2) that undergo spin transitions at different temperatures, correlating with the two-step conversion.
- Fe-N bond lengths change significantly between high-spin (HS) and low-spin (LS) states, confirming the spin state changes.
- DSC measurements provided thermodynamic data (enthalpy and entropy) for each step of the spin conversion.
Conclusions:
- The two-step spin conversion in [Fe(btr)(3)](ClO(4))(2) is attributed to the presence of two crystallographically distinct Fe(II) sites.
- The observed magnetic and structural behaviors are consistent with previous studies on two-step spin crossover systems.
- This compound serves as a model system for understanding complex spin transition mechanisms in iron(II) coordination compounds.