# Anion Binding by Macrocyclic Receptors: Computational Landscape of 1:1 and 2:1 Stoichiometries

## TL;DR

This paper explores how different macrocyclic receptors bind anions in various stoichiometries, showing how cavity size affects selectivity for anion sensing.

## Contribution

The study reveals distinct binding preferences of macrocycles for small and large anions, enabling versatile anion recognition strategies.

## Key findings

- Triazolophane preferentially binds small anions like chloride and bromide in 1:1 stoichiometry.
- Cyanostar and tricarb macrocycles favor larger anions like iodide in solution.
- Larger polyatomic anions form stable 2:1 sandwich complexes with macrocycles.

## Abstract

Macrocyclic receptors play a crucial role in supramolecular chemistry, enabling the selective binding of guest molecules through non‐covalent interactions. This study investigates the anion binding properties of three shape‐persistent macrocycles, triazolophane, cyanostar, and tricarb, each featuring preorganized cavities with polarized CH hydrogen bond donors. In the 1:1 binding stoichiometries, the macrocycles preferentially bind anions that fit inside their two‐dimensional cavities, with this preference being more pronounced in solution. Specifically, the triazolophane favors smaller anions like chloride and bromide, while the larger cavities offered by cyanostar and tricarb macrocycles preferentially bind the larger iodide. For large, polyatomic anions (SCN−, BF4
−, ClO4
−, and PF6
−), the macrocycles self‐assemble to form stable 2:1 sandwich complexes, exhibiting stronger binding. This shift in selectivity highlights the versatility of the macrocycles, making them promising candidates for anion sensing and regulation with various complexation stoichiometries.

Macrocyclic receptors with versatile binding stoichiometries. 1:1 complexes for small anions and 2:1 “sandwich” assemblies for large, weakly coordinating anions.