ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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

P. J. Srijana, B. S. Ooi, C. K. Quah, B. Narayana, B. K. Sarojini, and U. Likhitha

Department of Studies in Chemistry, Mangalore University, Mangalagangothri, India

E-mail: nbadiadka@gmail.com

Received: 19 September 2024  Accepted: 11 July 2025

Abstract:

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

Keywords: Flunarizine; Meclizine; Picric acid; Molecular salt; Single-crystal XRD; Hirshfeld surfaces analysis

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04249-4

Chemical Papers 79 (10) 7099–7115 (2025)