Mixed-valence ruthenium complexes rotating through a conformational Robin-Day continuum.

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Diruthenium complexes exhibit mixed-valence character, crucial for their electronic and spectroscopic properties.
• Understanding conformational effects on electronic structure is key to interpreting experimental data.

Purpose of the Study:

• To investigate the conformational energy landscape of mixed-valence diruthenium complexes.
• To correlate electronic structure, conformation, and spectroscopic properties (UV/Vis/NIR, IR).
• To elucidate the factors governing valence localization versus delocalization in these systems.

Main Methods:

• Utilized a nonstandard hybrid density functional (BLYP35 with 35% exact exchange).
• Employed continuum solvent models for calculations.
• Analyzed conformational phase space, electronic structure, and spin-density distributions.

Main Results:

• Lowest-energy conformers of complexes [1](+) and [2](+) show delocalized electronic structures.
• Conformational flexibility and bridging ligand orientation induce low-energy valence-trapped states.
• These valence-trapped states explain complex spectroscopic features, including NIR absorption shoulders and IR spectra.

Conclusions:

• Conformational effects are critical for understanding the electronic and spectroscopic behavior of mixed-valence diruthenium complexes.
• Thermally accessible valence-trapped conformations play a significant role in observed spectral characteristics.
• The Creutz-Taube ion [3](5+) also has low-lying valence-trapped states, but their spectroscopic impact is minimal.