Crystallographic and Computational Insights into Hydrogen Bonding in Diisopropylammonium Hydrogenophthalate

Abstract

Hydrogen bonds of the type A–H⋯A′, where A and A′ represent electronegative atoms, have attracted considerable attention in recent years due to their crucial role in stabilizing molecular systems. The combination of experimental characteristics and sophisticated quantum chemical calculations provides solid confirmation of the structural and electronic properties of the new molecules. In this context, diisopropylammonium hydrogenophthalate was synthesized and experimentally characterized, then studied by quantum chemistry in order to optimize its geometry and evaluate hydrogen-bonding interactions. X-ray diffraction analysis revealed the formation of parallel zigzag chains, stabilized by N–H···O hydrogen bonds between the diisopropylammonium cation and the hydrogenophthalate anion. Another intramolecular O–H···O hydrogen bond was also identified within the anion. From a theoretical perspective, the Mulliken charges, spectroscopic vibrations, and various global descriptors of the compound were studied using different basis sets within the DFT/B3LYP framework. The calculated vibrational frequencies were used to simulate infrared spectra for all basis sets considered. All these results confirm that diisopropylammonium hydrogenophthalate exists in the form of a salt, stabilized by a hydrogen bond between the cation and the anion. Finally, the frontier orbital energies (HOMO and LUMO), the energy gap, and global descriptors were determined in order to predict the reactivity of the compound. These findings provide a detailed understanding of how hydrogen bonding influences phthalate-based molecular crystals. They also highlight their potential for molecular electronics, advancing scientific knowledge.