Single crystal investigation, Hirshfeld surface analysis and DFT exploration of the pyrimethamine-based novel organic salt: 2, 4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium 3-carboxybenzoate hydrate (1:1:1)

Abstract Pyrimethamine was previously used for malaria treatment. It is not recommended nowadays for this purpose due to the developed drug resistance. In the current research work we are reporting the synthesis of pyrimethamine-based novel organic salt: 2, 4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium 3-carboxybenzoate hydrate (1:1:1) (DECH). The organic salt was synthesized from the acid base reaction of pyrimethamine and isophthalic acid. The structure of the accomplished DECH was verified unambiguously by the single crystal X-ray diffraction (SC-XRD) analysis. The SC-XRD investigation shows that the anion and cation counterparts of the organic salt form infinite 2D network due to the N-H⋯O, C-H⋯O and O-H⋯O bonding. The weak interaction of the type C-O⋯π is also assisting the strengthening of crystal lattice of the DECH. The molecular geometry of the compound in the ground state was calculated by using the density functional theory (DFT) method with 6–311++G(d,p) basis set and were compared with the experimental data. Additionally, HOMO–LUMO energy gap and molecular electrostatic potential (MEP) properties of the compound were performed at B3LYP/6–311++G(d,p) level. Hirshfeld surface analysis of the investigated DECH was used to confirm the existence, strength and order of intermolecular interactions in the compound. The title organic salt appears to be stable high reactive nucleophile.