Ionic Recognition Controlled by Conformational Change: A DFT Investigation

TL;DR

This paper explores how molecular conformations affect the recognition of cations and anions, offering insights for designing functional materials.

Contribution

The study reveals how conformational changes influence ion recognition mechanisms through electrostatic and orbital interactions.

Findings

Conformer 1 preferentially recognizes cations like K+ due to stronger electrostatic N···.cation interactions.

Conformer 2 favors anion recognition, particularly Br–, via favorable C–H···.anion interactions.

Electron-donor groups enhance cation recognition, while electron-acceptor groups improve anion recognition.

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.

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