X-ray structure of the water soluble [adeninium][p-sulfonatocalix[4]arene] which displays cationic and anionic bilayers

Treatment of Na-4[p-sulfonatocalix[4]arene]. nH(2)O with adenine in an acidic medium generates the water soluble [C5H6N5+](4)[p-sulfonatocalix[4]arene]. 14H(2)O. The compound crystallizes from solution in the space group P1 with a 12.824(2), b = 13.778(1), c = 19.536(2) Angstrom, alpha = 77.85(1), alpha = 78.78(1), gamma = 80.25(1)degrees, 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 pi 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.