Interaction geometry in hydrogen-bond donor-anion complexes: Acidity-dependent formation, fluctuation, and disruption

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Organic Chemistry

Background:

• The hexafluoroisopropyl alcohol (HFIP) group is a potent hydrogen-bond donor.
• Understanding how hydrogen-bond donors influence molecular interactions is crucial in chemistry.

Purpose of the Study:

• Investigate the role of hydrogen-bond donor acidity on interaction geometry in anion complexes.
• Analyze geometric formation, anchor constraints, and fluctuations in model systems.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Three model systems with varying hydrogen-bond donor acidities were studied: HFIP-substituted ethylbenzene, ethylphenol, and ethylbenzene.
• Analysis focused on geometric parameters rather than energy rankings.

Main Results:

• A strong O-H···O hydrogen-bond anchor in HFIP-substituted ethylbenzene led to anchor-dominated geometry with limited secondary C-H···O contact variability.
• A weaker anchor in ethylphenol allowed reproducible secondary interactions and some structural variability.
• Ethylbenzene, lacking a primary anchor, exhibited dispersed geometries due to multiple weak interactions.

Conclusions:

• Hydrogen-bond donor acidity dictates the strength of anchor constraints and geometric tolerance.
• Distinct interaction geometry regimes are formed, separated by geometric boundary regions, based on donor acidity.