Adjustable chiral self-sorting and self-discriminating behaviour between diamond-like Tröger's base-linked cryptands

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Crystallography

Background:

• Tröger's base derivatives are known for their unique structural motifs.
• Chiral cryptands with multiple stereocenters are of significant interest in molecular recognition and self-assembly.
• Understanding chiral behavior in complex molecular architectures is crucial for developing advanced materials.

Purpose of the Study:

• To synthesize novel Tröger's base-linked cryptands with two chiral N-centers.
• To investigate the self-sorting and self-discriminating behaviors of these cryptands in the solid state.
• To explore the influence of protonation on the crystallization of chiral molecules.

Main Methods:

• Synthesis of Tröger's base-linked cryptands (5a and 5b).
• Single-crystal X-ray diffraction analysis.
• Chiral crystallization studies under different conditions (racemic and protonated).

Main Results:

• Two isomers of Tröger's base-linked cryptands, 5a and 5b, were successfully synthesized, featuring rare diamond-like scaffolds with two chiral N-centers.
• Crystallization of racemic 5a (rac-5a) yielded a single enantiomer (RNRN-5a), demonstrating chiral self-sorting.
• Protonation of rac-5a with trifluoroacetic acid (CF3COOH) led to the co-crystallization of both enantiomers in pairs, indicating chiral self-discrimination.

Conclusions:

• Tröger's base-linked cryptands possess unique chiral properties that can be controlled by external stimuli like protonation.
• The observed chiral self-sorting and self-discriminating behaviors highlight the potential of these molecules in chiral recognition and crystal engineering.
• This study provides insights into the delicate balance governing enantiomeric interactions in crystal formation.