Deuteron quadrupole coupling constants and reorientational correlation times in protic ionic liquids

Area of Science:

• Physical Chemistry
• Materials Science
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Protic ionic liquids (PILs) are versatile materials with unique properties.
• Accurate determination of molecular dynamics in PILs is crucial for understanding their behavior.
• Deuteron quadrupole coupling constants (χD) provide insights into local molecular environments.

Purpose of the Study:

• To present an accurate method for determining deuteron quadrupole coupling constants (χD) for N-D bonds in triethylammonium-based PILs.
• To establish a correlation between χD and proton chemical shifts (δ(1)H) for PILs.
• To derive reorientational correlation times (τND) and characterize molecular dynamics in PILs.

Main Methods:

• Utilizing a linear relationship between deuteron quadrupole coupling constants (χD) and proton chemical shifts (δ(1)H).
• Employing Density Functional Theory (DFT) calculations on varying cluster sizes.
• Performing Nuclear Magnetic Resonance (NMR) deuteron quadrupole relaxation time measurements.

Main Results:

• Achieved accurate χD values ranging from 152 to 204 kHz for various PILs.
• Demonstrated that cation-anion interaction strength and hydrogen bonding influence χD.
• Confirmed the fulfillment of the extreme narrowing condition for the studied PILs.
• Estimated cluster sizes in PILs using correlation times and viscosity.

Conclusions:

• The developed method provides a reliable way to estimate χD in PILs via NMR.
• Molecular dynamics simulations complement NMR data in characterizing H-bonded aggregates.
• Understanding molecular dynamics and cluster formation is key to tailoring PIL properties.