(TAML)FeIV O complex in aqueous solution: synthesis and spectroscopic and computational characterization

Area of Science:

• Bioinorganic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Iron complexes with tetraamido macrocyclic ligands (TAMLs) are known to activate peroxides.
• Previous work characterized the S = 1/2 iron(V) complex [Fe(V)(O)B*](-).

Purpose of the Study:

• To synthesize and characterize the one-electron reduced species, [Fe(IV)(O)B*](2-) (2).
• To investigate the electronic structure and bonding of the Fe(IV) complex.
• To explore the pH-dependent behavior and potential for hydrogen bonding.

Main Methods:

• Synthesis of [Fe(IV)(O)B*](2-) via oxidation of [Fe(III)(H2O)B*](-) using tert-butyl hydroperoxide.
• Mössbauer spectroscopy to determine spin state and magnetic properties.
• Fe K-edge EXAFS analysis to determine Fe-O bond distance.
• Density Functional Theory (DFT) calculations for structural and electronic analysis.

Main Results:

• The S = 1 iron(IV) complex [Fe(IV)(O)B*](2-) was prepared in high yield (>95%) in aqueous solution at pH > 12.
• Mössbauer spectroscopy confirmed a S = 1 Fe(IV) state with specific quadrupole splitting and isomer shift values.
• Fe K-edge EXAFS analysis revealed a Fe(IV)-O bond distance of 1.69(2) Å.
• DFT calculations, including hydrogen bonding, accurately reproduced experimental data and indicated strong electron donation from the TAML ligand to the iron center.

Conclusions:

• The characterization of [Fe(IV)(O)B*](2-) provides insights into the electronic structure of high-valent iron-oxo species.
• The complex exhibits pH-dependent monomer-dimer equilibrium, relevant for its solution behavior.
• DFT calculations highlight the importance of ligand donation and solvent interactions in stabilizing the Fe(IV) state.