Asymmetry in angular rigidity of hydrogen-bonded complexes.

Area of Science:

• Chemical Physics
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Hydrogen bonding is fundamental in chemistry and biology.
• Hydrogen fluoride (HF) binary complexes exhibit unique properties due to strong hydrogen bonds.
• Understanding angular rigidity is key to characterizing intermolecular interactions.

Purpose of the Study:

• To investigate the asymmetry in angular rigidity between the proton donor (HF) and proton acceptor in hydrogen-bonded complexes.
• To quantify the relationship between intermolecular bending frequency and dissociation energy.
• To compare the angular rigidity of different proton acceptors, particularly nitrogen- and oxygen-based molecules.

Main Methods:

• Analysis of intermolecular bending frequencies.
• Calculation of bending elastic constants.
• Correlation of these parameters with dissociation energies.

Main Results:

• A linear relationship was found between the bending frequency of HF (proton donor) and the square root of dissociation energy.
• The angular rigidity of the proton acceptor is significantly lower than that of HF.
• The asymmetry ratio (bending elastic constants of HF/acceptor) generally exceeds 2, reaching over 20 in some cases.
• Nitrogen-bridged acceptors exhibit nearly ten times greater angular rigidity than oxygen-bridged acceptors.

Conclusions:

• The study quantifies a significant and variable asymmetry in angular rigidity within hydrogen-bonded HF complexes.
• The nature of the proton acceptor atom (N vs. O) strongly influences the angular rigidity.
• These findings provide insights into the nature of hydrogen bonding and intermolecular forces.