Triethylamine-Based Salts: Protic Ionic Liquids or Molecular Complexes?

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Amines and protic acids can form hydrogen-bonded complexes or protic ionic liquids (PILs) via proton transfer.
• Understanding the degree of proton transfer is crucial for designing new materials with specific properties.

Purpose of the Study:

• To investigate the proton transfer degree between triethylamine (TEA) and various protic acids.
• To characterize the resulting hydrogen-bonded complexes and protic ionic liquids (PILs).

Main Methods:

• Density Functional Theory (DFT) calculations, including B3LYP-GD3 method.
• Quantum Theory of Atoms in Molecules (QTAIM) for hydrogen bond analysis.
• Experimental characterization: thermal analysis (phase transition, destruction temperatures) and physicochemical measurements (conductivity, viscosity).

Main Results:

• TEA with acetic and propionic acids forms hydrogen-bonded complexes.
• TEA with benzoic acid shows complex behavior, with DFT favoring molecular complexes and experimental data suggesting PILs.
• TEA with hydrochloric, nitric, phosphoric, and salicylic acids forms salts, confirmed by both calculations and experiments.
• Calculated geometric and energy parameters of hydrogen bonds in complexes and ion pairs.

Conclusions:

• The degree of proton transfer from acids to TEA varies, leading to distinct hydrogen-bonded complexes, ion pairs, or protic ionic liquids.
• Combined computational and experimental approaches are effective in elucidating proton transfer mechanisms and material properties.
• The study provides insights into the formation and characteristics of TEA-acid adducts, relevant for ionic liquid and supramolecular chemistry research.