Vibrational solvatochromism in Vaska's complex adducts

Area of Science:

• Organometallic Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Vaska's complex (VC), bis(triphenylphosphine) iridium(I) carbonyl chloride, is a well-studied organometallic compound.
• Solvatochromism, the change in spectral properties due to solvent interactions, is crucial for understanding molecular behavior in solution.
• The vibrational spectra of metal carbonyl complexes are sensitive probes of electronic structure and bonding.

Purpose of the Study:

• To investigate the vibrational solvatochromism of Vaska's complex and its various adducts.
• To determine the influence of solvent properties on the carbonyl stretching frequency (ν(CO)).
• To elucidate the electronic interactions between the metal center, ligands, and solvent molecules.

Main Methods:

• Fourier Transform Infrared (FTIR) spectroscopy was employed to measure carbonyl stretching frequencies.
• Measurements were conducted across 16 diverse organic solvents with varying Lewis acidities.
• Density Functional Theory (DFT) calculations were performed to model solvent effects and aid spectral interpretation.

Main Results:

• The carbonyl stretching frequency (ν(CO)) of the dioxygen adduct (VC-O(2)) showed significant sensitivity to solvent electrophilicity.
• Minimal correlation between ν(CO) and solvent properties was observed for Vaska's complex and other adducts.
• An inverse relationship was found between the ν(CO) and the stretching frequency of the trans-O(2) ligand, indicating indirect modulation of metal-to-CO back-bonding.

Conclusions:

• The dioxygen ligand in Vaska's complex adducts plays a key role in mediating solvent interactions.
• Specific solvent interactions, particularly hydrogen bonding, strongly influence the electronic properties of the VC-O(2) complex.
• The binding mode of the O(2) ligand facilitates a more direct electronic communication with metal d-orbitals involved in carbonyl back-bonding compared to monatomic ligands.