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The effective preparation of pyrimethamine based co‐crystal salts with substituted benzoic acids (4‐nitrobenzoic acid 1 and 5‐chlorosalicylic acid 2) in methanol has been reported. The crystal structure of salt 1 and 2 is acquired through the x‐rays diffraction technique. Hirshfeld surface analysis elaborates the comparative study of the non‐covalent interactions in salt 1 and 2. In order to theoretically evaluate the non‐covalent interactions between molecular ions in salts 1 and 2, DFT and TD‐DFT calculations of molecular salts were performed. FMO and GRD analyses were performed to evaluate the reactivity of molecular ions. While, NBO, AIM and NCI analyses were performed to explore the non‐covalent interactions between cation and anions of molecular salts 1 and 2. The calculations demonstrated that salt 1 has H‐bond slightly stronger than salt 2 due to the withdrawing effect of ‐NO2 substituent group. The molecular anions reactivity allows different patterns of non‐covalent interactions that affect the salts arrangement in the crystal.

The effective preparation of two new pyrimidine- and pyridine-based organic crystalline salts with substituted acidic moieties (i.e., (Z)-4-(naphthalen-2-ylamino)-4-oxobut-2-enoic acid (DCNO) and 2-hydroxy-3,5-dinitrobenzoic acid (PCNP)) using methanol as a solvent has been reported. These molecular salts have ionic interactions that are responsible for their structural stabilization in their solid-state assemblies. The crystal structures of DCNO and PCNP were determined by the single-crystal X-ray diffraction (SCXRD) technique. The SCXRD study inferred that cations and anions are strongly packed due to N–H···O, N–H···N, and C–H···O noncovalent interactions in DCNO, whereas in PCNP, N–H···N noncovalent interactions are absent. The noncovalent interactions in both organic crystalline salts were comprehensively investigated by Hirshfeld surface analysis. Further, a detailed density functional theory (DFT) study of both compounds was performed. The optimized structures of both compounds supported the existence of the H-bonding and weak dispersion interactions in the synthesized organic crystalline salt structures. Both compounds were shown to have large and noticeably different HOMO/LUMO energy gaps. The atomic charge analysis results supported the SCXRD and HSA results, showing the formation of intermolecular noncovalent interactions in both organic crystalline salts. The results of the natural bond orbital (NBO) analysis confirmed the existence of (relatively weak) noncovalent interactions between the cation and anion moieties of their organic crystalline salts. The global reactivity parameters (GRPs) analysis showed that both organic crystalline salts’ compounds should be quite thermodynamically stable and that DCNO should be less reactive than PCNP. For both compounds, the molecular electrostatic potential (MEP) analysis results support the existence of intermolecular electrostatic interactions in their organic crystalline salts.

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