Three modes of interactions between anions and phenolic macrocycles: a comparative study

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Organic Chemistry

Background:

• Macrocyclic polyphenolic compounds, specifically resorcin[4]arenes, are recognized for their potential as multidentate anion receptors.
• Understanding the intricate binding motifs and interactions is crucial for designing selective anion sensors and receptors.

Purpose of the Study:

• To systematically analyze the binding modes between resorcin[4]arene derivatives and various anions.
• To investigate the role of supporting interactions, such as CH donors and ion pairing, in anion complexation.
• To evaluate the relative strength and solvent dependence of different binding modes.

Main Methods:

• Integration of new experimental data with existing literature, including solution data and crystal structures from the Cambridge Crystallographic Data Centre (CCDC).
• Utilized proton nuclear magnetic resonance (¹H NMR) and Diffusion Ordered Spectroscopy (DOSY) to identify and characterize binding modes.
• Analysis of anion binding in medium polarity solvents like tetrahydrofuran (THF) with tetraalkylammonium salts (Alk₄NX).

Main Results:

• Three distinct binding modes (Mode I, II, and III) were identified, driven by anion binding in THF.
• Mode I (unsubstituted resorcinarenes) involves OH and aromatic CH donors for multidentate, multivalent binding.
• Mode II (halogenated resorcinarenes) utilizes OH and aliphatic CH donors for weaker, more selective binding (effective for chlorides).
• Mode III (O-substituted derivatives) features anions nested by lower-rim aromatic CH donors in a multidentate, monovalent manner.
• The relative strength, solvent dependence, and crystallographic evidence for these binding modes were evaluated.

Conclusions:

• Resorcinarene derivatives exhibit versatile anion binding capabilities through multiple modes, influenced by structural modifications and solvent environment.
• The identified binding modes offer insights into the design of tailored anion receptors with tunable selectivity and strength.
• The study highlights the interplay between hydrogen bonding, CH-anion interactions, and ion pairing in supramolecular complexation.