Structural studies on two new molecular salts of drug molecules: Flunarizinium picrate and Meclizinium picrate

The study focuses on the structural and analytical characterization of two newly synthesized molecular salts: flunarizinium picrate (FLUPA) and meclizinium picrate (MECPA). It is confirmed that both FLUPA and MECPA are crystallized in the monoclinic system with \(\text{P}{2}_{1}/c\) and C2/c, respectively. Variations in bond lengths and angles confirm proton transfer from picric acid (PA) to the flunarizine (FLU)/meclizine (MEC) molecules. A bifurcated N−H⋯O intermolecular linkages was observed in between the FLU/MEC cation and picrate anion in both molecular salts. Two adjacent binary heterosynthons are identified, with graph sets \({R}_{2}^{2}\left(8\right)\) and \({R}_{2}^{2}\left(9\right)\) connecting C−H⋯O interactions between FLU and PA. Meanwhile, the FLU molecules are also interconnected through C−H⋯F linkages, as confirmed by the 11.7% contribution of F…H to the 2D fingerprint plot. Each picrate ion in MECPA is connected to neighboring MEC ions via N−H⋯O and C−H⋯O interactions, forming \({R}_{2}^{1}\)(6) and \({R}_{2}^{2}\)(8) ring motifs, hence stabilizing the crystal packing. The evidence for the formation of strong hydrogen bonds through N−H⋯O interactions was confirmed by IR and density functional theory analysis. The significant contribution of H∙∙∙H, O∙∙∙H, C∙∙∙H and F…H intercontacts to 2D fingerprint plot confirms the importance of N−H⋯O, C−H⋯O and C−H⋯F (FLUPA) interactions in stabilizing the supramolecular assembly. The bowtie patterns with colored segments (red and blue) observed on the shape index diagram of FLUPA and MECPA suggested the existence of π⋯π stacking interactions which is further supported by the curvedness plots. A detailed analysis of the supramolecular packing of FLUPA and MECPA is presented.

Graphical abstract