Rhenium-based molecular rectangles as frameworks for ligand-centered mixed valency and optical electron transfer

Area of Science:

• Inorganic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Tetrametallic molecular rectangles offer tunable frameworks for electronic studies.
• Mixed-valence compounds with ligand-based redox centers are rare and underexplored.
• Understanding electronic communication in such systems is crucial for molecular electronics.

Purpose of the Study:

• To synthesize and characterize a series of neutral, tetrametallic molecular rectangles.
• To investigate the electronic communication and redox properties of these novel compounds.
• To correlate structural features with electronic communication strengths.

Main Methods:

• Synthesis of six neutral, tetrametallic molecular rectangles with the general form ([Re(CO)(3)](2)BiBzIm)(2)-mu,mu'-(LL)(2).
• X-ray crystallography to determine the precise geometric structures and dimensions of the rectangle frameworks.
• Spectroscopic techniques to determine electronic strengths (H(ab)2) of the singly reduced compounds.
• Computational modeling to analyze geometric factors influencing electronic communication.

Main Results:

• Successfully synthesized six molecular rectangles with varying dimensions (5.7 Å x 7.2 Å to 5.7 Å x 19.8 Å).
• Identified the singly reduced rectangles as mixed-valence compounds where ligands act as redox centers.
• Observed a 100-fold variation in electronic strengths (H(ab)2) despite similar coordination environments.
• Correlated variations in electronic communication with specific geometric configurational differences.

Conclusions:

• The synthesized molecular rectangles provide a unique platform for studying ligand-based electronic communication.
• Direct ligand orbital overlap, rather than metal-mediated superexchange, governs electronic communication.
• Subtle geometric variations significantly impact the efficiency of interligand electronic communication, offering a pathway for molecular design.