Cooperativity between two types of hydrogen bond in H(3)C-HCN-HCN and H(3)C-HNC-HNC complexes

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Interactions

Background:

• Hydrogen bonding is crucial in molecular interactions.
• Understanding cooperative effects in hydrogen-bonded systems is key to predicting molecular behavior.
• Acetonitrile (CH3CN) and its isomers (HCN, HNC) form relevant hydrogen-bonded complexes.

Purpose of the Study:

• To investigate cooperative effects in hydrogen-bonded clusters involving acetonitrile.
• To quantitatively analyze the impact of cooperativity on interaction energies.
• To explore the role of cooperativity in single-electron hydrogen bonds versus traditional hydrogen bonds.

Main Methods:

• Ab initio calculations were employed to study molecular clusters.
• The MP2 level of theory with the aug-cc-pVTZ basis set was used for optimizations and frequency calculations.
• Analysis included interaction energies, NMR chemical shifts, charge transfers, and topological parameters.

Main Results:

• Optimized structures and harmonic vibrational frequencies were determined for various clusters.
• Cooperative effects contributed approximately 10% to the interaction energy in CH3CN-HCN-HCN.
• Cooperativity contributed about 15% in the CH3CN-HNC-HNC complex, showing a larger effect than in binary complexes.

Conclusions:

• Cooperative effects play a significant role in the stability of these hydrogen-bonded systems.
• The magnitude of cooperativity is greater in complexes with single-electron hydrogen bonds compared to HCN-HCN and HNC-HNC.
• Computational data, including NMR shifts and charge transfers, support the findings on cooperative interactions.