Fine Tuning of the Redox-Active Diguanidine Ligand in Cationic Cobalt Complexes for Electronic Structure Control

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Hexacoordinated cobalt complexes offer tunable redox properties.
• Redox-active ligands can influence metal-centered and ligand-centered redox events.
• Controlling electron transfer pathways is crucial for advanced materials.

Purpose of the Study:

• To investigate the redox chemistry of hexacoordinated cobalt complexes with redox-active diguanidine ligands.
• To demonstrate the ability to tune the site of one-electron oxidation (ligand- or metal-centered).
• To explore the design of bistable cobalt-guanidine complexes for potential spin-switching applications.

Main Methods:

• Synthesis of hexacoordinated cobalt complexes featuring redox-active diguanidine ligands.
• Systematic modification of diguanidine ligands and co-ligands.
• Electrochemical studies to probe redox behavior.
• Quantum-chemical calculations to analyze electronic structures and energy levels.

Main Results:

• Tuning of diguanidine and co-ligands directed one-electron oxidation to be ligand- or metal-centered.
• Achieved high-spin Co^II complexes with oxidized diguanidine ligands (ligand-centered oxidation).
• Achieved low-spin Co^III complexes with reduced diguanidine ligands (metal-centered oxidation).
• Fine-tuning led to bistable systems with energetically proximate redox isomers, resulting in mixtures of both oxidation states.
• Quantum-chemical calculations supported the energetic proximity of redox isomers.

Conclusions:

• Demonstrated a directed approach to controlling redox chemistry in cobalt-guanidine complexes.
• Established a method for designing bistable cobalt complexes by harmonizing redox isomer energies.
• Highlighted the potential of these complexes in the development of spin-switching devices.