Abrupt spin crossover in iron(iii) complexes with aromatic anions.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Spin crossover (SCO) complexes are molecular materials that can switch between low-spin and high-spin states.
• Designing SCO materials with cooperative behavior is crucial for advanced applications.
• The role of intermolecular interactions, such as halogen bonds and pi-pi stacking, in influencing SCO properties is an active area of research.

Purpose of the Study:

• To synthesize and characterize novel iron(iii) spin crossover complexes.
• To investigate the structural features, including pi-pi chains and halogen bonds, that influence spin crossover behavior.
• To evaluate the effectiveness of aromatic anions in promoting cooperative spin crossover.

Main Methods:

• Synthesis and full characterization of two iron(iii) spin crossover complexes: [Fe(qsal-X)2]OTs·nH2O (X = Br, I).
• Single-crystal X-ray diffraction to determine the solid-state structures, revealing 1D pi-pi chains and halogen bonds.
• Magnetic susceptibility measurements to study the spin crossover phenomenon and determine transition temperatures.

Main Results:

• The synthesized complexes, [Fe(qsal-Br)2]OTs·H2O (1·H2O) and [Fe(qsal-I)2]OTs·2H2O (2·2H2O), were fully characterized.
• Structural analysis revealed 1D pi-pi chains linking Fe(iii) centers and strong halogen bonds, with chains angled due to C-HX interactions.
• Abrupt spin crossover was observed in both complexes: for 1, T1/2↓ = 258 K and T1/2↑ = 260 K; for 2, T1/2 = 298 K. The transition temperature increased from Br to I.

Conclusions:

• The study successfully prepared and characterized two iron(iii) spin crossover complexes.
• Structural features, including pi-pi chains and halogen bonds, play a significant role in the observed spin crossover behavior.
• Aromatic anions are effective components for designing cooperative spin crossover systems, as demonstrated by the abrupt SCO in both synthesized complexes.