A highly efficient, preorganized macrobicyclic receptor for halides based on CH... and NH...anion interactions

Area of Science:

• Supramolecular Chemistry
• Anion Recognition
• Organic Synthesis

Background:

• Developing selective anion receptors is crucial for sensing and separation.
• Macrobicyclic cryptands are known for strong anion binding but often require multiple donor groups.
• Hydrogen bonding interactions play a key role in anion recognition.

Purpose of the Study:

• To synthesize and characterize a novel macrobicyclic azaphane (1) for anion binding.
• To evaluate the binding affinity and selectivity of azaphane 1 for various anions, particularly fluoride.
• To elucidate the structural basis of anion recognition in the macrobicyclic system.

Main Methods:

• Synthesis of macrobicyclic azaphane 1 via a tripod-tripod cyclization reaction.
• Crystallographic analysis of key intermediates and anion complexes.
• Potentiometric titrations to determine binding constants and selectivity.

Main Results:

• Azaphane 1 demonstrates strong and selective binding for fluoride and chloride anions.
• Binding constants reveal high affinity, with F(-)/Cl(-) selectivity exceeding five logarithmic units.
• X-ray crystallography confirms the formation of inclusive 1:1 complexes with halide anions.
• The preorganized structure of azaphane 1 compensates for the weaker intrinsic affinity of CH hydrogen bond donors.

Conclusions:

• The macrobicyclic azaphane 1 represents a highly effective anion receptor, particularly for fluoride.
• The study highlights the importance of preorganization in enhancing anion binding affinity.
• Structural insights reveal the interplay of NH, CH hydrogen bonding, and anion-pi interactions in determining complex geometry and selectivity.