Dimensional caging of polyiodides: cation-templated synthesis using bipyridinium salts

The potential of bipyridinium derivatives in the cation templated synthesis of polyiodides has been explored by applying the strategy of size-matching between cations and anions. Bipyridinium cations 1-4, bearing benzyl and functionalized benzyl pendants at nitrogen atoms, are able to template the selective formation of I(4)(2-) and I(3)(-) species. Thanks to the supramolecular space compartmentation induced by the benzyl pendants, the formation of I(4)(2-) and I(3)(-) is independent of the stoichiometry adopted in the crystallization procedure. Bipyridinium cation 5, bearing methyl pendants, is unable to induce space compartmentation and different polyiodides are obtained depending on the stoichiometry used in the crystallization process as the cation-anion size-matching alone does not control the polyiodide formation.