Mapping Bridge Conformational Effects on Electronic Coupling in Mo₂-Mo₂ Mixed-Valence Systems.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Electronic coupling between metal centers is crucial for molecular electronics and catalysis.
• Bridging ligands significantly influence the electronic communication in dinuclear complexes.
• Previous studies explored phenylene and naphthalene linkers, establishing a basis for comparison.

Purpose of the Study:

• To synthesize and characterize novel dimolybdenum (Mo₂) dimers bridged by 9,10-anthracenedicarboxylate and its thiolated derivatives.
• To investigate the impact of bridging ligand conformation on the electronic coupling between Mo₂ units.
• To systematically map the effects of bridge structure on electronic coupling strength and electron transfer mechanisms.

Main Methods:

• Synthesis of three Mo₂ dimers: [Mo₂(DAniF)₃]₂(μ-9,10-O₂CC₁₄H₈CO₂), [Mo₂(DAniF)₃]₂(μ-9,10-OSCC₁₄H₈COS), and [Mo₂(DAniF)₃]₂(μ-9,10-S₂CC₁₄H₈CS₂).
• Spectroscopic analysis (near-IR) to study mixed-valence complexes and intervalence charge transfer.
• Density Functional Theory (DFT) calculations to correlate electronic properties with bridge conformation (torsion angle ϕ).

Main Results:

• Mo₂ dimers exhibited significant deviation of the anthracene ring from planarity (torsion angles 50-76°).
• Absence of intervalence charge transfer absorptions in near-IR spectra, classifying complexes as Class I (Robin-Day scheme).
• Electronic coupling strength showed a linear relationship with cos² ϕ, decreasing in the order phenylene > naphthalene > anthracene.

Conclusions:

• The conformation of the bridging ligand strongly modulates electronic coupling in Mo₂ dimers.
• The results support a through-bond superexchange mechanism for electronic coupling and electron transfer.
• This study provides a systematic framework for understanding bridge conformation effects on electronic communication in dinuclear complexes.