Anion-π interactions in supramolecular architectures.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Coordination Chemistry

Background:

• Anion-π interactions, complementary to cation-π interactions, are increasingly recognized as significant noncovalent forces.
• These interactions were previously overlooked due to their counterintuitive nature but are now known to be energetically favorable.
• Anions play vital roles in chemical and biological processes, making anion recognition and transport key research areas.

Purpose of the Study:

• To investigate unprecedented supramolecular systems driven by anion-π contacts.
• To explore the interplay between ligand π-acidity, anion identity, and metal ions in self-assembled architectures.
• To demonstrate the potential of anion-π interactions in designing selective anion receptors and sensors.

Main Methods:

• Synthesis and characterization of metallacycles using transition metal ions and π-acidic ligands (bptz, bmtz, bppn, HAT(CN)6).
• X-ray crystallography, NMR spectroscopy (¹⁹F, ¹³C, halogen), mass spectrometry (MS), and cyclic voltammetry (CV) for structural and electronic analysis.
• Density Functional Theory (DFT) calculations to corroborate experimental findings on anion-π contacts.

Main Results:

• Tetrahedral and octahedral anions templated discrete molecular squares and pentagons, respectively, with encapsulated anions forming close anion-π contacts critical for stability.
• Ligand π-acidity influenced the self-assembled structures, with higher π-acidity favoring propeller-type complexes and lower π-acidity favoring grid structures.
• The extended π-acidic heterocycle HAT(CN)6 formed highly colored complexes with halide ions, exhibiting strong charge-transfer and anion-π contacts, indicating potential for anion sensing.

Conclusions:

• Anion-π contacts are essential for the stability and templation of metallacycles, influencing their nuclearity and structure.
• The judicious choice of ligands and metal ions allows for the rational design of supramolecular architectures with tunable properties.
• Anion-π interactions offer a promising platform for developing advanced materials, including highly sensitive anion receptors and colorimetric sensors.