Probing interactions within liquid media via a model H-bond donor-acceptor mixture

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Solvent Effects

Background:

• Understanding liquid interactions is crucial for controlling physicochemical properties.
• Hexamethylphosphoramide (HMPA) is a strong H-bond acceptor, while 2,2,2-trifluoroethanol (TFE) is a strong H-bond donor.
• Assessing solvent-solvent interactions in mixtures is key to predicting bulk properties.

Purpose of the Study:

• To investigate the solute-solvent and solvent-solvent interactions in HMPA + TFE mixtures.
• To characterize the changes in hydrogen bonding, polarity, and viscosity upon mixing.
• To understand the synergistic effects on Kamlet-Taft parameters.

Main Methods:

• Solvatochromic UV-Vis absorbance probes (Kamlet-Taft parameters).
• Photoinduced charge-transfer and fluorescence polarity probes.
• FTIR and Raman spectroscopy.
• Viscosity and excess molar volume measurements.
• Intramolecular excimer-forming fluorescence probes.

Main Results:

• Kamlet-Taft parameters (α and β) show positive synergism in TFE-rich and HMPA-rich regions, respectively.
• Mixture dipolarity (π*) is lower than predicted, indicating a significant non-polar character.
• Spectroscopic data suggest weakened H-bonds between TFE and HMPA molecules.
• Positive excess molar volumes and viscosities confirm weakened interactions in the mixture.
• Microfluidity measurements support the formation of a less polar liquid milieu.

Conclusions:

• Mixing HMPA and TFE leads to a less polar liquid than anticipated, despite their individual polarities.
• Synergistic effects on hydrogen bond acidity and basicity are observed.
• Weakened intermolecular interactions and a less polar environment are characteristic of HMPA + TFE mixtures.