A conformationally flexible, urea-based tripodal anion receptor: solid-state, solution, and theoretical studies

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Crystallography

Background:

• Tripodal tris(urea) receptors with pyridinium functionalities were synthesized.
• These receptors feature a hexasubstituted aryl core, incorporating both urea and pyridinium groups.

Purpose of the Study:

• To synthesize and characterize novel tripodal tris(urea) cationic receptors.
• To investigate the anion binding behavior and conformational flexibility of these receptors with various anionic guests.

Main Methods:

• Synthesis of tripodal tris(urea) cationic receptors.
• X-ray crystallography for characterizing host-anion complexes.
• Solution 1H NMR spectroscopy for binding studies and conformational analysis.
• Density functional theory computations for geometric analysis.

Main Results:

• Receptors 1 and 2 were synthesized with p-tolyl and octyl substituents, respectively.
• X-ray crystallography revealed distinct geometries for complexes like 1-(Br)3 and 1-(PF6)3.2(CH3)2CO, indicating anion-dependent flexibility.
• NMR studies confirmed significant affinity for halides and hydrogen sulfate, highlighting CH...X- interactions.
• Computational studies elucidated preferred conformations for host-chloride complexes, suggesting unimolecular capsule formation.

Conclusions:

• Tripodal tris(urea) receptors exhibit remarkable conformational flexibility in response to different anionic guests.
• Both NH and CH donors play crucial roles in stabilizing host-anion interactions.
• The study provides insights into the design of receptors capable of selective anion recognition and encapsulation.