Cooperativity in hydrogen-bonded interactions: ab initio and "atoms in molecules" analyses

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Hydrogen bonding plays a crucial role in molecular interactions.
• Understanding cooperative effects is key to characterizing complex chemical systems.
• The H(2)CO...(HF)(n) system presents an interesting model for studying these phenomena.

Purpose of the Study:

• To investigate the nature and strength of hydrogen bonds in H(2)CO...(HF)(n) complexes.
• To quantify the impact of cooperativity on hydrogen bond characteristics.
• To explore the transition towards covalent interactions in these complexes.

Main Methods:

• Utilized the MP2 (Møller–Plesset perturbation theory) method for electronic structure calculations.
• Employed various basis sets including 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ.
• Applied the scheme of decomposition of interaction energy and Bader theory (Quantum Theory of Atoms in Molecules).

Main Results:

• Observed significant enhancement of the F-H...O hydrogen bond due to cooperativity.
• Identified a covalent character in stronger hydrogen bonds within the complexes.
• Found that delocalization energy increases with cooperativity and stronger hydrogen bonds.
• Noted a negative electronic energy density at the bond critical point for strong hydrogen bonds, indicating partial covalency.

Conclusions:

• Cooperativity significantly strengthens hydrogen bonds in H(2)CO...(HF)(n) complexes, leading to a partial covalent nature.
• The balance between delocalization and electrostatic energy shifts towards delocalization in stronger hydrogen bonds.
• Bader theory confirms the partly covalent character of these enhanced hydrogen bonds.