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

Abstract

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[CA 4 •LiI 4 ], and catena-poly[tetra(cyanuric acid)•sodium tetraiodide], n[CA 4 •NaI 4 ], featuring threedimensional (3D) cationic frameworks able to segregate linear, infinite n[I 4 − ] chains in their squared open channels and the layered solid [CA•KI 3 ] 2 •I 2 •2H 2 O characterized by alternating sheets of (i) hydrated potassium cations and CA molecules and (ii) I 3 − anions and discrete I 2 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).

Comparison of N···I and N···O Halogen Bonds in Organoiodine Cocrystals of Heterocyclic Aromatic Diazine Mono-N-oxides

“…Of the halogens, the highly polarizable diiodine molecule typically forms stronger interactions and is less prone to oxidation of the electron pair donor molecule, which makes diiodine, and polyiodides in general, useful choices for halogen-bonding-directed crystal engineering. − However, diiodine is still a potent oxidizer and, thus, can be limited in its potential utility as a supramolecular building block. These limitations can be addressed by utilizing other forms of iodine that are less oxidizing, such as organoiodines. − By inserting an organic ‘spacer’ between the two iodine atoms, the functionality of a polarized iodine atom can be retained while it exhibits less oxidation strength.…”