A new air-stable cyclohexasulfur(cyclo-S
6)was discovered in the crystal of 3,5-diphenyl-1,2,4-dithiazol-1-ium(dpdti)iodide, formed by cocrystallization. The dpdti was synthesized via an oxidation reaction of thiobenzamide with iodine in benzene. Two kinds of crystal habits—brock-shaped(crystal-
A)and needle-shaped(crystal-
B)—were obtained following recrystallization from acetonitrile solvent. All molecules in crystal-
A and -
B were identified through single-crystal X-ray structure analysis using a synchrotron X-ray. The cyclic-S
6 molecule in the crystal-
A is a self-assembly enclosed by the dpdti cation and iodide anion, and is assumed to contribute to their stability in the crystal, akin to the S
n ring in zeolites and sodalites. In the context of cyclo-S
6, cocrystallization is constituted by weak intermolecular effects such as the van der Waals force. Crystal engineering of cocrystals resulted in air-stable cyclo-S
6. This study presents a method to turn an unstable molecule into a stable crystalline molecule that maintains its origin structure, with an aim of predicting its stability in future studies.
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