Iodine Clathrated: A Solid-State Analogue of the Iodine-Starch Complex

Co-crystallizing iodine with a simple dicationic salt (1,8-diammoniumoctane chloride) results in the clathration of the iodine (I₂ ) molecules inside trigonal and hexagonal helical channels of the crystal lattice with 72 wt % overall I₂ loading. The I₂ inside the bigger trigonal channel forms a I-I⋅⋅⋅I-I⋅⋅⋅I-I halogen-bonded infinite helical chain, while the I₂ in the smaller hexagonal channel is disordered. In both channels the I₂ interaction with the channel wall happens through I-I⋅⋅⋅Cl^- halogen bonds. The helical channels in the crystal lattice are constructed via the strong charge-assisted H₂ N⁺ H⋅⋅⋅Cl^- hydrogen bonds between the dications and the chloride anions. The structure shows a marked similarity with the well-known starch-I₂ system, and thus may provide insight for the yet unresolved structure of the I₂ in the helical starch channel.