Water channel formation in supramolecular assemblies containing sulfonated calix[4]arene

Abstract

We report the crystallographic characterization of three supramolecular complexes involving p-sulfonatocalix[4]arene (SC4) and two different symmetrically shaped cations as guest molecules. Complex I crystallizes in the monoclinic space group C2/m, forming a bilayer structure with bis-imidazolium cations effectively encapsulated within two SC4 cavities, resulting in a stable molecular capsule. Complex II, crystallizing in the triclinic space group P-1, exhibits similar structural features, with bis-imidazolium cations encapsulated by two SC4 molecules within the bilayer arrangement. Both Complexes I and II have the bis-imidazolium cation in a syn conformation relative to the central benzene ring. In contrast, Complex III crystallizes in the monoclinic space group C2/c and contains a Co(III) sarcophagine cation within the SC4 cavity, but without the formation of a molecular capsule. Despite this, it retains the bilayer arrangement, though in a wavy configuration. All structures display water channels containing water molecules in close proximity to atoms at the distances close to hydrogen bonding in an extended packing. Extensive hydrogen bonding between water molecules and SC4 sulfonate groups contributes significantly to the overall stability of the crystal lattice. These findings highlight the versatility of SC4 in accommodating different guest molecules, ranging from imidazolium-based cations to larger metal complexes, and demonstrates the importance of non-covalent interactions in stabilizing the supramolecular architectures.