Molecular structures, hydrogen bonding and electrostatic interactions of 3-(2-bromo-pyridinium)-propionic acid and 3-(pyridinium)-pivalic acid halides

Intra- and intermolecular interactions and the conformations of 3-(2-bromo-pyridinium)-propionic acid bromide (1) and 3-(pyridinium)-pivalic acid chloride (2) have been studied by X-ray diffraction and theoretically. In these complexes, Br⁻ and Cl⁻ anions are H-bonded to the COOH group and interact electrostatically with the positively charged nitrogen atoms of neighbouring molecules. To analyse these interactions theoretically, the structures of monomers and dimers in various configurations were optimized by PM3 and BLYP/6-31G(d,p) methods. The analysis confirmed the vital role of both the H-bonds and electrostatic interactions (intra- and intermolecular) for the molecular conformation and the ionic aggregation in the solid state.