Charge-Assisted Anion-π Interaction and Hydrogen Bonding Involving Alkylpyridinium Cations.

Competition and cooperation of charge-assisted anion-π interactions and hydrogen bonding were explored in the solid state and in solutions of 1-ethyl-4-carbomethoxypyridinium iodide, the compound utilized by Kosower to calculate solvent polarity Z-indices. X-ray structural analysis of this salt revealed multiple short contacts of iodide anions with hydrogen atoms and aromatic rings of pyridinium cations. Geometric characteristics, quantum theory of atoms in molecules (QTAIM), and noncovalent interaction (NCI) analysis of these contacts indicated comparable interaction energies of the anion-π and hydrogen bonding between iodide and pyridinium cation.