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Axial Redox Tuning at a Tetragonal Cobalt Center
Jonghoon Choi1, Sun Hee Kim2, Yunho Lee1
1Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea.
Inorganic Chemistry
|March 31, 2021
Summary
Square pyramidal cobalt complexes exhibit remarkable multielectron redox activity, tunable via axial donors. These stable complexes show three reversible redox events, demonstrating significant electrochemical potential for advanced applications.
Area of Science:
- Inorganic Chemistry
- Electrochemistry
- Materials Science
Background:
- Square pyramidal cobalt complexes are synthesized to investigate their multielectron redox properties.
- A stable redox-active cobalt complex is constructed using a tridentate 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide (acriPNP-) ligand combined with bidentate ligands.
Purpose of the Study:
- To explore the multielectron redox behavior of novel square pyramidal cobalt complexes.
- To tune the redox potential of the Co(II/I) couple by modifying the axial donor.
- To investigate the electronic structure and electrochemical stability of these cobalt complexes.
Main Methods:
- Synthesis of square pyramidal cobalt complexes with acriPNP- and various bidentate ligands.
- Electrochemical measurements (cyclic voltammetry) in tetrahydrofuran (THF) to determine redox potentials and reversibility.
- Structural, spectroscopic, and theoretical analyses to examine the electronic structure.
Main Results:
- Tuning the axial donor successfully shifted the Co(II) to Co(I) reduction potential from -2.6 V (neutral) to -3.4 V (anionic).
- Three fully reversible redox events were observed between -3.0 V and 0.0 V vs Fc/Fc+ over 100 cycles, indicating high electrochemical stability.
- The acriPNP ligand's oxidation potential varied significantly (-2.4 V to +0.15 V), influenced by cobalt's contribution to the amido-based molecular orbital.
Conclusions:
- Square pyramidal cobalt complexes with acriPNP- ligands display robust multielectron redox activity and tunable potentials.
- The observed redox behavior is attributed to the interplay between the cobalt center and ligand-based orbitals.
- These findings highlight the potential of these complexes in electrochemical applications requiring stable redox-active materials.
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