Deciphering supramolecular synthons in OXYMA-B salts: Crystallographic characterization and theoretical evaluation of hydrogen bond networks

Abstract

Four new crystal structures of OXYMA-B in its anionic form have been synthesized and structurally characterized via single-crystal X-ray diffraction. The new salts incorporate protonated amine-based cations including 1-phenylpiperazine (1PP), 1,4-dioxa-8-azaspiro[4.5]decane (DASD), ethylenediamine (ETDA), and pyrrolidine (Pyr), which function as efficient hydrogen bond (H-bond) donors. The electron-rich nature of the OXYMA-B anion provides multiple sites for H-bond acceptance, leading to diverse supramolecular synthons including (5),(6), (8) and(12). The theoretical component of this study is based on density functional theory (DFT) calculations to dissect and characterize the individual H-bonded synthons using the quantum theory of atoms in molecules (QTAIM) framework. Additionally, interaction energies of discrete H-bonds have been quantified to rationalize their strength and directional preferences, showing that directional NH···O bonds contribute the most to the stability of the assemblies, with ancillary contacts playing a secondary but supportive role. The total interaction energies range from –34.0 to –50.0 kcal/mol, underscoring the critical role of hydrogen bonding in dictating the supramolecular architectures. This combined experimental–computational approach sheds light on the structural determinants driving supramolecular organization in OXYMA-B-based salts and highlights their potential for crystal engineering applications.