The Ionic Hydrogen/Deuterium Bonds between Diammoniumalkane Dications and Halide Anions

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Ionic hydrogen bonds (IHBs) are crucial in various chemical and biological systems.
• Measuring IHB stretching frequencies directly can be challenging due to spectral limitations.

Purpose of the Study:

• To investigate halide-anion binding to different diammonium compounds.
• To characterize the ionic deuterium bond (IDB) stretching frequencies and their dependencies.

Main Methods:

• Infrared multiple-photon dissociation (IRMPD) spectroscopy in the 1000-2250 cm^-1 range.
• Theoretical calculations to complement experimental spectroscopic data.
• Deuterium exchange to shift measurable frequencies.

Main Results:

• IDB stretching frequencies were successfully measured by deuterium exchange, falling within the experimental range.
• Frequency shifts indicate decreasing halide-anion-deuterium bond strength with increasing halide size and ammonium methylation.
• Alkane chain length influences IDB frequency due to geometric constraints and affects Fermi resonance band positions.

Conclusions:

• The study provides a detailed understanding of halide-anion interactions in diammonium systems.
• Deuterium labeling is an effective strategy for probing IHBs beyond spectral limitations.
• The findings contribute to the fundamental knowledge of non-covalent interactions and their spectroscopic signatures.