Elucidation of the Role of Structure and Energetics in the Crystal Chemistry of Novel Dihydropyrimidinium-Based Organic salts

In this work, we present a comprehensive experimental and theoretical investigation of five newly synthesized dihydropyrimidinium-based organic salts, focusing on their structural arrangement and energetic properties. Single-crystal X-ray diffraction reveals that the solid-state structures crystallized in the triclinic or monoclinic crystal systems with a common dihydropyrimidinium cationic core, substituted with different groups (−CN, –Br, –NO 2, and –F). A detailed PIXEL energy decomposition and distance–energy (R/E) plots reveal that strong N–H···Cl – and C–H···Cl – contacts play a pivotal role in stabilization through large Coulombic and dispersion contributions. In contrast, the cation–cation pairs are largely destabilizing but partially compensated by π···π stacking, C–H···O/N, C–H···F, and C–H···π interactions. Fingerprint-plot analyses indicate the presence of H···Cl contacts as primary contributors in the anionic environment, while H···O, H···F, H···C, and H···N interactions show a variation within the cationic fragments. Quantitative comparison across the series reveals that substituent variation alters both the nature and magnitude of ionic and dispersive interactions, leading to variations in packing motifs. This research provides valuable insights into the energetic balance of organic salts, offering a framework for the crystal engineering of stable pharmaceutical solid forms.