Gas-phase lithium cation basicity: revisiting the high basicity range by experiment and theory

Area of Science:

• Physical Chemistry
• Gas-Phase Ion Chemistry

Background:

• Previous FT-ICR lithium cation basicity (LiCB) scales at 373 K showed a systematic downward bias in the upper range.
• Understanding the accurate basicity of ligands is crucial for various chemical applications.

Purpose of the Study:

• To identify the source of systematic differences in previously published LiCB scales.
• To establish a more accurate and reliable LiCB scale at 373 K.

Main Methods:

• Experimental measurement of LiCB values for 31 ligands using proton-transfer equilibrium techniques at 373 K.
• Construction of a self-consistent LiCB scale anchored to pyridine.
• Kinetic modeling to assess the impact of Li(+) bound dimers on equilibrium measurements.

Main Results:

• New experimental LiCB values were determined for ligands ranging from tetrahydrofuran to 1,2-dimethoxyethane.
• The newly established LiCB scale shows good agreement with G2(MP2) theoretical calculations.
• Accurate equilibrium measurements are achievable with sufficient ion trapping time, even with dimer formation.

Conclusions:

• The systematic downward shift in previous LiCB scales originated from inaccurate temperature estimation and calibration issues in Cook's kinetic method.
• The new experimental LiCB scale provides a more reliable dataset for gas-phase basicity studies.
• Proper control of ion trapping time is essential for precise equilibrium measurements in FT-ICR studies.