Embroidering Ionic Cocrystals with Polyiodide Threads: The Peculiar Outcome of the Mechanochemical Reaction between Alkali Iodides and Cyanuric Acid

We report here the preparation and structural characterization of a series of new crystalline materials obtained by mechanochemical mixing of cyanuric acid (CA) and alkali halides (LiI, NaI, and KI) in the presence of molecular iodine, namely, the isomorphous catena-poly[tetra(cyanuric acid)·lithium tetraiodide], n[CA4·LiI4], and catena-poly[tetra(cyanuric acid)·sodium tetraiodide], n[CA4·NaI4], featuring three-dimensional (3D) cationic frameworks able to segregate linear, infinite n[I4-] chains in their squared open channels and the layered solid [CA·KI3]2·I2·2H2O characterized by alternating sheets of (i) hydrated potassium cations and CA molecules and (ii) I3- anions and discrete I2 molecules. The combination of X-ray diffraction (XRD), Raman spectroscopy, and thermal analyses allowed us to elucidate the compound's structural features and to discuss the effect of cation size on the stoichiometry and architecture of the three ionic cocrystals (ICCs).