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Enabling Valence Delocalization in Iron(III) Macrocyclic Complexes through Ring Unsaturation.
Reese A Clendening1, Stephanie S Delancey1, Andrew T Poore1
1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
Inorganic Chemistry
|June 30, 2023
Summary
The tetra-imino macrocycle HMTI promotes significant valence delocalization in iron complexes, unlike the tetra-aza macrocycle HMC. This difference in electronic structure influences electron delocalization and metal-orbital energies.
Area of Science:
- Coordination Chemistry
- Organometallic Chemistry
- Spectroelectrochemistry
Background:
- Iron complexes with macrocyclic ligands are crucial in various chemical and biological systems.
- Understanding electron delocalization in mixed-valent metal complexes is key to designing advanced materials.
- The electronic properties of macrocyclic ligands significantly influence metal center reactivity and redox behavior.
Purpose of the Study:
- To synthesize and characterize novel iron(III) complexes with tetra-imino (HMTI) and tetra-aza (HMC) macrocyclic ligands.
- To investigate the effect of macrocyclic ligand structure on valence delocalization in mixed-valent iron species.
- To elucidate the role of ligand π-acidity in modulating electronic communication within the complexes.
Main Methods:
- Synthesis and full characterization of iron(III) complexes [Fe(HMC)(C2DMA)2]CF3SO3 and [Fe(HMTI)(C2Y)2]CF3SO3.
- Vibrational and electronic absorption spectroelectrochemical analyses to study one-electron oxidation.
- Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy to probe electronic structure and metal properties.
Main Results:
- Significant valence delocalization was observed in HMTI-based complexes due to the tetra-imino macrocycle.
- Mixed-valent ions derived from the HMC-based complex exhibited more localized electronic character.
- The π-acidity of HMTI lowers Fe(III) dπ orbital energies compared to the σ-donating HMC ligand.
Conclusions:
- The tetra-imino macrocycle HMTI facilitates substantial valence delocalization across the -C2-FeIII-C2- bridge.
- Macrocycle-dependent valence delocalization is strongly influenced by ligand π-acidity and σ-donation.
- These findings provide insights into controlling electronic communication in iron-based molecular materials.
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