3.2. Synthesis, Crystallization, and Single Crystal X Ray Determination

Pyridine-3-carboxaldehyde (1.07 g, 0.01 mol) was added to a solution of adamantane-1-carbohydrazide (1.94 g, 0.01 mol), in ethanol (15 mL), and the mixture was heated under reflux for two hours. The mixture was then concentrated to half the original volume and water (5 mL) was added and allowed to stand overnight. The precipitated crude product was filtered, washed with water, dried, and crystallized from EtOH/H₂O to yield (2.32 g, 82%) of the monohydrate of compound 1 as transparent colorless needle crystals. The anhydrous compound was obtained after drying in a desiccator for 24 h. Mp: 185–187 °C. ¹H-NMR: δ 11.01 (s, 1H, NH), 8.81 (s, 1H, CH=N), 8.61 (s, 1H, Pyridine-H), 8.47 (d, 1H, Pyridine-H, J = 4.5 Hz), 8.01 (s, 1H, Pyridine-H), 7.48 (t, 1H, Pyridine-H, J = 4.5 Hz), 2.03 (s, 3H, Adamantane-H), 1.88 (s, 6H, adamantane-H), 1.72 (s, 6H, adamantane-H). ¹³C-NMR: δ 173.86 (C=O), 150.95, 149.05, 133.73, 130.79, 124.48 (Pyridine-C), 144.35 (CH=N), 39.77, 38.73, 36.53, 28.05 (adamantane-C).

5-Nitrothiophene-2-carboxaldehyde (1.57 g, 0.01 mol) was added to a solution of adamantane-1-carbohydrazide (1.94 g, 0.01 mol), in ethanol (15 mL), and the mixture was heated under reflux for one hour. On cooling, the precipitated crude product was filtered, washed with cold ethanol, dried, and crystallized from EtOH to yield (3.17 g, 95%) of compound 2 as transparent pale yellow crystals. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution of the title compound in EtOH/CHCl₃ (1:2, v/v) at room temperature. Mp: 233–235 °C. ¹H-NMR: δ 11.24 (s, 1H, NH), 8.68 (s, 1H, CH=N), 8.12 (d, 1H, Thiophene-H, J = 4.2 Hz), 7.51 (d, 1H, Thiophene-H, J = 4.2 Hz), 2.02 (s, 3H, Adamantane-H), 1.87 (s, 6H, adamantane-H), 1.68–1.73 (m, 6H, adamantane-H). ¹³C-NMR: δ 174.18 (C=O), 151.03, 147.73, 130.99, 129.58 (Thiophene-C), 140.63 (CH=N), 39.74, 38.55, 36.42, 27.96 (adamantane-C).

The selected suitable single crystals of compounds 1 and 2 were mounted using polybutene oil on a flexible loop fixed on a goniometer head and immediately transferred to the diffractometer. Pre-experiment, data collection, data reduction, and analytical absorption correction [45] were performed with the program suite CrysAlisPro [46] using the Olex2 program [47]. The structures were solved with the SHELXT [48] small molecule structure solution program and refined with the SHELXL 2018/3 program package [49] by full-matrix least-squares minimization on F². PLATON [50] was used to check the result of the X-ray analysis. For more details about the data collection and refinement parameters, see the CIF files.