Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand

Area of Science:

• Inorganic Chemistry
• Materials Science
• Electrochemistry

Background:

• Iron complexes with macrocyclic ligands are crucial in catalysis and materials science.
• Understanding redox behavior and spin states is key to designing functional molecules.

Purpose of the Study:

• To synthesize and characterize a novel iron(III) complex with a dibenzotetraethyltetraamido macrocyclic ligand (DTTM).
• To investigate the redox properties and electronic structure of the iron complex and its oxidized forms.
• To elucidate the nature of oxidation and spin state changes upon chemical oxidation.

Main Methods:

• Crystallography, spectroscopy (UV-Vis, X-ray absorption near-edge structure), electrochemistry (cyclic voltammetry), Mössbauer spectroscopy, and density functional theory (DFT) calculations.
• Synthesis and characterization of iron(III) complex (1) and its one-electron (2) and two-electron (3) oxidized species.
• Electrochemical and chemical oxidation studies to probe redox pathways.

Main Results:

• The iron(III) complex (1) exhibits a square-pyramidal structure and S = 3/2 spin state.
• Stepwise oxidation occurs at the ligand, not the iron center, with distinct spectral changes.
• Oxidized complexes (2 and 3) show ligand radical character and antiferromagnetic coupling with the iron(III) center.
• Iron centers remain in the intermediate-spin iron(III) state throughout the oxidation process.

Conclusions:

• The DTTM ligand facilitates reversible redox processes, enabling ligand-based oxidation.
• Antiferromagnetic coupling between ligand radicals and the iron(III) center is established in oxidized species.
• This work provides insights into the electronic structure and spin dynamics of iron-macrocycle complexes.