Electronic Coupling and Electron Transfer between Two Mo₂ Units through meta- and para-Phenylene Bridges

Area of Science:

• Inorganic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Dimeric metal complexes are crucial for understanding electron transfer (ET) processes.
• Electronic coupling (EC) dictates the rate of ET between metal centers.
• Bridging ligands significantly influence EC and ET dynamics.

Purpose of the Study:

• To investigate the impact of meta-phenylene bridges on EC and ET in Mo2 dimers compared to para isomers.
• To elucidate the mechanisms of electronic coupling in the absence of π conjugation.
• To correlate structural modifications with electron transfer kinetics.

Main Methods:

• Synthesis and optical analysis of mixed-valence Mo2 complexes with meta- and para-phenylene bridges.
• Spectroscopic characterization of electronic coupling parameters (H_ab).
• Calculation of electron transfer rates (k_et).
• Density Functional Theory (DFT) for computational analysis of coupling pathways.

Main Results:

• Meta-phenylene bridged Mo2 dimers exhibit significantly weaker EC and 2-3 orders of magnitude lower ET rates compared to para isomers.
• Para isomers show sensitivity to O/S alternation in the bridge, while meta analogues display similar EC and ET parameters (H_ab ≈ 300-400 cm⁻¹, k_et ≈ 10⁹ s⁻¹).
• DFT calculations reveal destructive quantum interference in meta series due to cancellation of π-conjugated pathways.

Conclusions:

• Meta-phenylene bridges effectively attenuate electronic coupling in Mo2 dimers.
• Through-σ-bond and/or through-space coupling become operative when π conjugation is disabled.
• Quantum interference plays a critical role in modulating electron transfer through meta-linked systems.