Matrix effects on hydrogen bonding and proton transfer in fluoropyridine - HCl complexes

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Hydrogen bonding interactions are fundamental in chemistry and biology.
• Fluorine substitution is known to modulate molecular properties, including hydrogen bond strength.
• Understanding these effects is crucial for designing molecules with specific properties.

Purpose of the Study:

• To investigate the impact of fluorine substitution on the hydrogen bond strength in pyridine-HCl complexes.
• To explore the influence of dielectric media on the structural and bonding properties of these complexes.
• To correlate computational findings with experimental spectroscopic data.

Main Methods:

• Matrix-isolation infrared (IR) spectroscopy was used to study solid neon, argon, and nitrogen complexes.
• Extensive quantum-chemical calculations were performed on pyridine-HCl and eight fluorinated analogs.
• Analysis included equilibrium structures, binding energies, bonding analyses, and the effects of dielectric media.

Main Results:

• Fluorination generally weakens hydrogen bonds in pyridine-HCl complexes, with 2,6-substitution showing the most pronounced effect.
• Matrix stabilization varies across different host environments, influencing hydrogen bond strength.
• Proton transfer to pyridine occurs in dielectric media for less fluorinated systems (e.g., pyridine-HCl, 3-fluoropyridine-HCl), while highly fluorinated systems remain intact.

Conclusions:

• Fluorine substitution systematically alters hydrogen bond strength in pyridine-HCl complexes.
• Dielectric environment plays a critical role in determining the nature of the hydrogen bond and potential proton transfer.
• Computational and spectroscopic results are consistent, providing a comprehensive understanding of these interactions.