Ionic Recognition Controlled by Conformational Change: A DFT Investigation

Abstract

Ions play a crucial role in the production of important materials and are associated with various health and environmental issues. Noncovalent interactions serve as fundamental tools for controlling the availability of cations and/or anions. Herein, we investigate the ability of two conformations of the 2,6-bis(1,2,3-triazol-4-yl)pyridine molecule to recognize cations (1), such as Li+, Na+, or K+, and anions (2), including F–, Cl–, or Br–. EDA-NOCV analysis demonstrates that the conformers preferentially recognize ions based on the size of the cations (K+ → Na+ → Li+) and anions (Br– → Cl– → F–). The preferential interaction with smaller cations (and anions) arises from the more attractive electrostatic and orbital interactions (N···.cation and C–H···.anion bonds). The presence of electron-donor groups (−NH2) in the first conformer (1) enhances cation recognition through stronger electrostatic N···.cation interactions. Conversely, the presence of electron-acceptor groups (−NO2) in the second conformer (2) facilitates anion recognition via more favorable electrostatic, orbital, and dispersion C–H···.anion interactions. Cation recognition is found to be more favorable in the first conformer than anion recognition in the second due to more attractive electrostatic energy and/or less Pauli repulsive energy associated with (O or primarily N)···.cation interactions in 1···.cations compared to (N or mainly C)–H···.anion bonds in 2···.anions. These findings provide significant insights into the mechanisms of cation and/or anion recognition through different conformations using the same base structure and can inform the design of molecules with enhanced functionalities.