Nonspherical anion sequestration by C-H hydrogen bonding.

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Host-Guest Chemistry

Background:

• Macrocyclic arenes are foundational to supramolecular chemistry, establishing principles of noncovalent interactions.
• The development of hosts for large, nonspherical anions remains a significant challenge in the field.

Purpose of the Study:

• To design and synthesize novel rigidified resorcin[4]arenes, termed fluorocages, for the selective recognition of large anions.
• To engineer the anion binding affinity of these hosts by modifying their internal cavity.
• To establish a tunable platform for anion sequestration through controlled C-H bond donor electropositivity.

Main Methods:

• Synthesis of rigidified resorcin[4]arenes with varying fluorine substitution.
• Spectroscopic and binding studies to determine anion association constants (Ka).
• Density Functional Theory (DFT) calculations to rationalize binding affinities through Hirshfeld Charges (HCs).

Main Results:

• A single synthetic step allowed for a seven-orders-of-magnitude variation in host anion affinity.
• Increased fluorine substitution in fluorocages led to enhanced anion association constants.
• Fluorocages demonstrated tunable binding, with weak-to-medium affinity for hexafluorophosphate ([PF6]-) and high affinity for methanesulfonate ([MeSO3]-).

Conclusions:

• Fluorocages represent a novel class of macrocyclic hosts engineered for large anion recognition.
• The electropositivity of aromatic C-H bond donors, tuned by fluorine substitution, is critical for controlling anion binding.
• This work provides a versatile platform for designing selective anion hosts in supramolecular chemistry.