Systematic experimental charge density analysis of anion receptor complexes.

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Crystallography

Background:

• Anion recognition is crucial in biological and chemical systems.
• Understanding intermolecular forces in host-guest complexes is essential for designing new materials.
• Previous studies often relied on geometric criteria for hydrogen bond identification.

Purpose of the Study:

• To systematically investigate hydrogen bonding in urea-based anion receptor complexes using electronic resolution.
• To quantify hydrogen bond strengths and contributions of various intermolecular forces.
• To assess the reliability of geometric criteria versus charge density studies for hydrogen bond characterization.

Main Methods:

• Systematic electronic resolution study.
• Bader's Quantum Theory of Atoms In Molecules (QTAIM) for hydrogen bond characterization.
• Charge density analysis and comparison of related complexes.
• Correlation of hydrogen bond strength with anion basicity and receptor structure.

Main Results:

• The strength of N-H···anion hydrogen bonds was quantified.
• Individual contributions of intermolecular forces were derived.
• Geometric criteria for hydrogen bonding were validated for strong interactions but found less reliable for weaker ones.
• Charge density studies confirmed weaker intermolecular interactions missed by geometric analysis.
• Receptor substitution patterns significantly impact supramolecular system properties.

Conclusions:

• High-resolution electronic studies provide a robust method for characterizing host-guest systems.
• Charge density analysis is vital for accurately identifying weaker hydrogen bonding interactions.
• Receptor design can be rationally guided by understanding the interplay of hydrogen bonding, anion basicity, and structural factors.