Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

Area of Science:

• Inorganic Chemistry
• Magnetochemistry
• Solid-State Physics

Background:

• Iron clusters are crucial in understanding magnetic interactions and electronic structures.
• Investigating complex magnetic behaviors in polynuclear iron compounds is essential for materials science.

Purpose of the Study:

• To synthesize and characterize a novel tri-iron cluster, [Fe3(μ3-O)(mpmae)2(OAc)2Cl3].
• To elucidate the electronic and magnetic ground state properties of the synthesized cluster.
• To correlate structural features with observed magnetic behavior.

Main Methods:

• X-ray crystallography for structural determination.
• Variable-frequency electron paramagnetic resonance (EPR) spectroscopy.
• Magnetic susceptibility and magnetization measurements.
• 57Fe Mössbauer spectroscopy.
• Theoretical analysis of electronic structure and magnetic interactions.

Main Results:

• The cluster [Fe3(μ3-O)(mpmae)2(OAc)2Cl3] was successfully synthesized and its structure determined.
• A total spin S_T = 5/2 ground state was confirmed, characterized by a negative, nearly axial zero-field splitting (D = -0.49 cm^-1).
• Strong antiferromagnetic coupling (J = 115(5) cm^-1) between two Fe(III) ions and weak coupling (j = 7(1) cm^-1) to the third site dictate the magnetic properties.
• Mössbauer spectroscopy revealed distinct internal magnetic fields at the iron sites, with two sites showing small, mixed-sign fields attributed to excited state mixing induced by structural distortion.

Conclusions:

• The magnetic properties are dominated by the weakly coupled iron site.
• Minute structural distortions play a significant role in inducing excited state mixing, influencing the observed magnetic fields.
• This study provides insights into the relationship between structure, electronic configuration, and magnetic behavior in polynuclear iron complexes.