Thermal monomerization unlocks 3/2 ↔ 5/2 spin crossover in a kinetically trapped high-spin Fe(III) dimer

Area of Science:

• Coordination Chemistry
• Materials Science
• Magnetochemistry

Background:

• Iron(III) complexes are crucial in developing switchable spin-state materials.
• Understanding the relationship between complex structure and spin state is key for material design.

Purpose of the Study:

• To report a novel iron(III) coordination system with thermally controlled dimer-to-monomer transformation.
• To investigate the accompanying changes in spin state and their relationship with nuclearity.
• To provide insights into designing switchable spin-state materials.

Main Methods:

• In situ generation of a tridentate ligand (HL) via condensation.
• Reaction of the ligand with Fe(NCSe)3 to form dimeric and monomeric complexes.
• Characterization of complexes and investigation of spin state changes using thermal methods.
• Theoretical calculations to rationalize experimental findings.

Main Results:

• A kinetically favored dimeric iron(III) complex [Fe2(L)2(OMe)2(NCSe)2]·MeOH was synthesized at room temperature, stabilizing a high-spin state.
• Upon heating, the dimer dissociates into a monomeric complex [Fe(L)2]NCSe, exhibiting spin crossover (SCO) behavior.
• The study demonstrates the interplay between nuclearity and spin states, showing kinetic trapping of high-spin states and thermal activation to SCO.

Conclusions:

• The research highlights how structural transformations (dimer-to-monomer) can control spin states in iron(III) complexes.
• This work provides a pathway for designing switchable spin-state materials by controlling nuclearity and thermal activation.
• The findings contribute to a deeper understanding of spin state control in coordination chemistry.