Molecular and ionic hydrogen bond formation in fluorous solvents

Area of Science:

• Supramolecular Chemistry
• Fluorous Chemistry
• Hydrogen Bonding

Background:

• Limited quantitative studies exist on noncovalent association in fluorous solvents.
• Understanding these interactions is crucial for applications in extraction, sensors, and crystal engineering.

Purpose of the Study:

• Investigate hydrogen bonding between N-heterocyclic bases and a carboxylic acid-terminated perfluoropolyether in fluorous solvents.
• Determine the conditions and stoichiometry of proton transfer in these complexes.

Main Methods:

• Continuous variations experiments to determine complex stoichiometry.
• UV-Vis and infrared (IR) spectroscopy to characterize complex type (molecular vs. ionic).
• Compilation and comparison of existing literature data on hydrogen bonding in various solvents.

Main Results:

• Weaker bases (e.g., pyrazine) form 1:1 molecular complexes (B.HA) in FC-72.
• Stronger bases (e.g., pyridine) form 1:3 ionic complexes (BH+.A-HAHA) in FC-72.
• Proton transfer in fluorous solvents requires a higher acid-to-base ratio (1:3) compared to polar (1:1) or nonpolar organic (1:2) solvents.

Conclusions:

• Stoichiometry and binding strength of noncovalent interactions are solvent-dependent.
• Fluorous solvents necessitate specific conditions for proton transfer in hydrogen bonds.
• This research provides insights into supramolecular chemistry in fluorous media.