Anion-anion proton transfer in hydrogen bonded complexes

Area of Science:

• Supramolecular Chemistry
• Anion Recognition
• Chemical Sensing

Background:

• Anion receptors are crucial for selective ion binding.
• Hydrogen bonding plays a key role in molecular recognition.
• Understanding phosphate complexation is vital in biological and chemical systems.

Purpose of the Study:

• To investigate the complexation of dihydrogen phosphate by a novel anion receptor.
• To elucidate the mechanism of unusual stoichiometry formation in anion binding.
• To explore the role of hydrogen bond donors in modulating pK(a) values.

Main Methods:

• Synthesis of a multi-donor anion receptor.
• Spectroscopic titration to determine binding constants and pK(a) shifts.
• X-ray crystallography to confirm solid-state complex structures.

Main Results:

• The anion receptor significantly reduced the pK(a) of dihydrogen phosphate.
• Addition of further dihydrogen phosphate led to deprotonation of the bound species.
• Formation of a monohydrogen phosphate receptor complex was confirmed by X-ray crystallography.
• Unusual binding stoichiometries were observed and explained by the deprotonation mechanism.

Conclusions:

• Multi-donor hydrogen bonding can effectively lower the acidity of bound anions.
• This deprotonation mechanism explains the formation of unexpected stoichiometries in anion-receptor interactions.
• The study provides insights into designing receptors for specific phosphate species.