Crystallographic Features, Synthon Investigation and Hirshfeld Surface Analysis of Two 3D Supramolecular Salts of Pyridine and Organic Carboxylic Acids Constructed by Classical H-Bonds and Some Noncovalent Interactions

Preparation, X-ray crystal structure, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis of complexes 1, 2 from the pyridine and the mono- and dicarboxylic acids are reported. XRD and FTIR analysis demonstrate that both belong to the organic salt. The salt 1 crystallizes in the triclinic, space group \(P\bar{1}\), with a = 7.271(3) Å, b = 9.548(4) Å, c = 14.698(7) Å, α = 78.435(6)°, β = 85.975(7)°, γ = 71.492(6)°, V = 948.0(8) Å³, Z = 2. The salt 2 crystallizes in the orthorhombic, space group P2₁2₁2₁, with a = 7.9476(6) Å, b = 11.6756(9) Å, c = 25.686(2) Å, α = β = γ = 90°, V = 2383.4(3) Å³, Z = 4. In this study, the pyridine at 1, 2 were both involved in the classical ionic N–H⋯O H-bonds. The O–H⋯O H-bonds were also present in both salts. Apart from the classical H-bonds, the auxiliary interactions of CH⋯O, CH₃–O, CH₃–CH_3, CH–π, and O–π also helped the stabilization and expansion of the whole high-dimensional (3D) packings. Hirshfeld surface analysis provides additional views into the prevalence of the various short contacts in the crystal structure. On account of the subtle balance of the various nonbonding associations the synthons \(R_{2}^{2}\)(7), \(R_{2}^{2}\)(10), \(R_{3}^{2}\)(8), \(R_{3}^{2}\)(10), \(R_{3}^{3}\)(9), \(R_{3}^{3}\)(19), \(R_{4}^{3}\)(15), \(R_{4}^{4}\)(17), \(R_{5}^{4}\)(12) and \(R_{6}^{4}\)(18) were noted at the salts. For the combination of the classical H-bonds plus the various non-covalent contacts, the salts adopted the 3D net. In conclusion, we have shown that 3D structures can be constructed by the collective non-covalent interactions.