Two-step spin transition around room temperature in a Fe^III complex

Area of Science:

• Molecular magnetism
• Coordination chemistry
• Materials science

Background:

• Spin-crossover (SCO) phenomena in iron(III) complexes are crucial for developing molecular switches and memory devices.
• Achieving room-temperature SCO is a significant challenge in molecular magnetism.
• Ligand design and crystal packing play vital roles in tuning SCO properties.

Purpose of the Study:

• To synthesize and characterize new iron(III) spin-crossover complexes.
• To investigate the influence of solvent molecules and counterions on SCO behavior.
• To explore the relationship between structural features and magnetic transitions.

Main Methods:

• Synthesis of two iron(III) complexes, [Fe(HL)2]·X·2MeCN (X = BF4− for 1, X = ClO4− for 2), using a substituted Hqsal ligand (H2L).
• Single-crystal X-ray diffraction for structural analysis, focusing on hydrogen bonding interactions.
• Variable-temperature magnetic susceptibility measurements to study spin transitions and hysteresis.

Main Results:

• Both complexes exhibited one-step SCO below room temperature with distinct hysteresis loop widths (10 K for 1, 4 K for 2).
• Solvent removal led to significant changes: complex 1 showed two-step SCO around room temperature with wider hysteresis (32 and 62 K), while complex 2 maintained one-step SCO.
• Structural analysis confirmed that solvent and counteranion interactions via hydrogen bonding influence the SCO properties.

Conclusions:

• The study demonstrates the critical role of solvent molecules and hydrogen bonding in modulating spin-crossover behavior in iron(III) complexes.
• Tailoring crystal packing and intermolecular interactions can facilitate SCO transitions at or near room temperature.
• These findings provide insights for designing advanced molecular materials with tunable magnetic properties.