Unraveling the noncovalent interactions in a organic crystal using Quantum theory of atoms in molecules

Abstract

X-ray diffraction analysis, combined with the Quantum Theory of Atoms in Molecules (QTAIM), serves as a powerful tool for describing chemical bonding in real space for solids. By integrating theoretical and experimental data, a more accurate representation of atomic interactions including Van der Waals forces, hydrogen bonds, covalent, ionic, and metallic bonds is achieved. The analysis of noncovalent interactions through electronic density enables the identification of Lewis acid and base sites, while also revealing the directional ‘key-lock’ interactions that correspond to molecular recognition. The examination of critical points in the electron density and its derivatives allows for the characterization of the types of interactions present in crystal packing. This study focuses on the experimental and theoretical investigation of noncovalent interactions within a molecular crystal of a newly synthesized carbohydrazide derivative. The crystal structure was determined using X-ray single-crystal diffraction, and the crystallographic asymmetric unit was optimized via DFT, with the results compared to experimental data. Noncovalent interactions in real space such as Van der Waals forces, hydrogen bonds, and inter- and intramolecular steric repulsions were analyzed in terms of electron density and its derivatives. The QTAIM framework was applied to quantify the strength of these interactions, employing Voronoi deformation density and electron localization and delocalization indices for solids. The results presented in this work, using crystal engineering, reveal that derivatives of diurea compounds crystallize following a characteristic pattern that forms a synthon configuration. The strength of this interaction, quantified through QTAIM analysis of the electronic density, provides a deeper understanding of the chemistry of these compounds, both in terms of biological activity and coordination chemistry.