Iron(II) Spin Crossover Complexes Based on a Redox Active Equatorial Schiff-Base-Like Ligand

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Iron(II) complexes are known for spin crossover (SCO) properties, crucial for molecular switches.
• Incorporating redox-active units like tetrathiafulvalene (TTF) can modulate SCO behavior and introduce new functionalities.
• Schiff base ligands offer versatile coordination environments for metal ions.

Purpose of the Study:

• To synthesize and characterize novel iron(II) coordination compounds featuring a redox-active TTF-containing ligand.
• To investigate the spin transition behavior and its relationship with electronic and optical properties.
• To explore the interplay between the iron center's redox state and the TTF unit's redox activity.

Main Methods:

• Synthesis of a N2O2 coordinating Schiff base ligand with a TTF unit and axial ligands (pyridine or bpee).
• Characterization using single X-ray structure analysis, magnetic susceptibility, temperature-dependent UV-vis spectroscopy, cyclic voltammetry, and Mössbauer spectroscopy.
• Spectroelectrochemical studies to probe redox-induced spectral changes.

Main Results:

• Two iron(II) complexes, [FeTTFL(py)2] and {[FeTTFL(bpee)]}, were successfully synthesized.
• Both complexes exhibit spin transition behavior below room temperature (T1/2 = 146 and 156 K).
• Redox behavior reveals three reversible steps at the iron center and TTF unit, with electronic coupling observed.

Conclusions:

• The synthesized iron(II) complexes demonstrate tunable spin crossover properties modulated by the TTF unit.
• The interplay between iron-centered redox processes and TTF oxidation leads to coupled optical changes.
• These findings highlight the potential of TTF-functionalized coordination compounds for developing advanced functional materials.