Mercaptopyridines, heteroaromatic compounds containing thiol groups, are widely studied for their applications in coordination chemistry, supramolecular design and materials science due to their selective binding properties and photoresponsiveness. In this work, we investigated the crystallization of 4-mercaptopyridine with cyanuric acid under strictly controlled conditions. A solution of both components in aqueous ethanol was subjected to UV irradiation and then allowed to crystallize slowly at 4 °C, followed by ambient conditions. Three crystalline products were isolated and were structurally characterized, namely, a cocrystal of cyanuric acid with 1,2-di(pyridin-4-yl)disulfane, C10H8N2S2·C3H3N3O3, (I), a cocrystal of cyanuric acid with di(pyridin-4-yl)sulfane, C10H8N2S·C3H3N3O3, (II), and a new 3:2 cocrystal of cyanuric acid with di(pyridin-4-yl)sulfane, 2C10H8N2S·3C3H3N3O3, (III). No crystalline material was obtained under dark conditions, and cocrystal (III) was observed only after UV irradiation, which also yielded larger and better-quality single crystals than visible light. The results are consistent with oxidative coupling of 4-mercaptopyridine in solution under the applied conditions, giving disulfane and sulfane species that subsequently cocrystallize with cyanuric acid. Two of the cocrystals correspond to previously reported forms CSD refcodes KIRGIF and KIRGOL; Gogoi et al. (2023). J. Mol. Struct. 1289, 135806, whereas cocrystal (III) is reported here for the first time.
Książkiewicz et al. (Fri,) studied this question.