X-ray Structure of the Water Soluble [Adeninium]-[p-Sulfonatocalix[4]arene] which Displays Cationic and Anionic Bilayers

Abstract

Treatment of Na₄[p-sulfonatocalix[4]arene]·nH₂O with adenine in an acidic medium generates the water soluble [C₅H₆N₅ ⁺]₄[p-sulfonatocalix[4]arene]·14H₂O. The compound crystallizes from solution in the space group P1 with a = 12.824(2), b = 13.778(1), c = 19.536(2) Å, α = 77.85(1), α = 78.78(1), γ = 80.25(1)°, and D_c = 1.557 gcm⁻³ for Z = 2 (C₄₈H₇₂O₃₀N₂₀S₄). Refinement based on 9639 observed reflections led to R = 0.065. The complex crystallizes with a water molecule exhibiting aromatic π hydrogen bonding imbedded within the hydrophobic calixarene cavity. The four adeninium ions form a hydrogen bonded array in a layer external to the cavity. The overall structure exists as bilayers of anionic calix[4]arenes in the cone conformation. These layers are intercalated with bilayers of cationic adeninium ions and are separated by a bed of water molecules. The bilayer structure has been observed in other calix[4]arene complexes, and the intercalation of a cationic bilayer further enhances the similarity in structure of the water-soluble calix[4]arenes to that of clays.