Supramolecular Assembly and Ab Initio Quantum Chemical Calculations of 2-Hydroxyethylammonium Salts of <i>para</i>-Substituted Benzoic Acids

Crystal structures of seven salts of 2-hydroxyethylamine with benzoic acid (1) and different substituted benzoic acids, such as p-methylbenzoic acid (2), p-methoxybenzoic acid (3), p-hydroxybenzoic acid (4), p-chlorobenzoic acid (5), p-bromobenzoic (6), and p-iodobenzoic (7) have been studied. The salts units of 1–7 serve as building blocks (BB) of the supramolecular architecture. In a crystal they are held together via proton-transferred N–H···O and normal O–H···O hydrogen bonds. The substituents on anions influence dipole–dipole interactions between anions and cations in molecular aggregates. As a result, they are organized in building blocks either via one charge-assisted (1, 2) hydrogen bond or via two (3–7) hydrogen bonds. The dispersion interaction significantly contributes to intermolecular force fields driving the organization of hydrogen bonds in BB. In all studied compounds, building blocks are consolidated into 2-D layers through the N–H···O and O–H···O hydrogen bonds. For the crystal structures of 2–7, with non-centrosymmetric space groups and the BB self-assembled by two hydrogen bonds, the macroscopic polarizations of a unit cell is practically perpendicular to the layers.

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