Hydrazine-mediated strongly coupled Re(CO)3 dimers

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Computational Chemistry

Background:

• Dimeric metal complexes can display coupling interactions mediated by bridging ligands.
• Schiff base ligands are versatile in coordinating metal ions and influencing their electronic properties.

Purpose of the Study:

• To synthesize and characterize two rhenium(III) carbonyl dimers bridged by a bis(pyridine-2-carbaldehyde imine) hydrazine ligand.
• To investigate the electronic coupling and redox behavior of these dimeric complexes.
• To elucidate the electronic structure and the origin of the observed coupling using computational methods.

Main Methods:

• Synthesis of rhenium(III) carbonyl dimers.
• Cyclic voltammetry to study redox properties and electronic coupling.
• Spectroelectrochemistry to detect mixed-valence states and inter-valence charge-transfer (IVCT) bands.
• Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) for electronic structure calculations.

Main Results:

• Successful synthesis of two Re(CO)3 dimers linked by a bis(pyca) hydrazine Schiff base ligand.
• Observation of strong electronic coupling across the dimer, evidenced by large separation in reduction potentials (∼480 mV) and high comproportionation constants (∼1.5 × 10^8).
• Spectroelectrochemistry confirmed a mixed-valence state upon reduction, with a distinct IVCT band.
• DFT calculations revealed that reduction occurs at the diimine units, indicating ligand-based electronic coupling.

Conclusions:

• The bis(pyca) hydrazine Schiff base ligand effectively mediates strong electronic coupling between the two rhenium centers in the dimeric complexes.
• The observed coupling is primarily a ligand-based phenomenon, influencing the electronic communication between the metal centers.
• The study provides insights into the design of multinuclear complexes with tunable electronic properties through ligand choice.