Theoretical, Solid-State, and Solution Quantification of the Hydrogen Bond-Enhanced Halogen Bond

Area of Science:

• Supramolecular Chemistry
• Chemical Physics
• Crystallography

Background:

• Noncovalent forces are fundamental in natural systems.
• Understanding the interplay of proximal forces like hydrogen and halogen bonds is critical.
• Previous studies lacked experimental quantification of synergistic effects between hydrogen and halogen bonds.

Purpose of the Study:

• To experimentally quantify the Hydrogen Bond-Enhanced Halogen Bond (HBeXB) phenomenon.
• To investigate the influence of hydrogen bond donors on halogen bond strength.
• To provide a foundational understanding of HBeXBs independent of complex biological structures.

Main Methods:

• Theoretical calculations to predict the influence of hydrogen bond donors on halogen bond strength.
• X-ray crystallography to analyze the structural characteristics of HBeXBs in halide complexes (Br-, I-).
• 19F NMR titrations to experimentally measure binding affinities in HBeXB analogues.

Main Results:

• Theoretical studies indicate electron-rich halogen bond donors and stronger hydrogen bond donors maximally enhance halogen bonds.
• X-ray structures reveal HBeXBs result in shorter halogen bonds compared to analogues lacking hydrogen bonding.
• 19F NMR titrations demonstrate significantly stronger binding for the HBeXB analogue with chloride.

Conclusions:

• The study experimentally validates the existence and strengthening effect of Hydrogen Bond-Enhanced Halogen Bonds (HBeXBs).
• HBeXBs exhibit enhanced binding properties, offering shorter bond lengths and stronger interactions.
• These findings establish a basis for future research into the synergistic effects of proximate hydrogen and halogen bonds.