SUPRAMOLECULAR CHEMISTRY OF P-SULFONATOCALIX[5] ARENE - A WATER-SOLUBLE, BOWL-SHAPED HOST WITH A LARGE MOLECULAR CAVITY

The first X-ray crystallographic studies are reported for water-solubl e inclusion complexes of the macrocyclic p-sulfonatocalix[5]arene(1) ( 1b). The complexes Na-7[p-sulfonatocalix[5]arene]. 18H(2)O (2) and Na- 5[p-sulfonatocalix[5]arene]. py-N-O . 8.5H(2)O (3) containing water an d pyridine N-oxide (py-N-O) guest species have been isolated. In 2 the large bowl-shaped cavity of the host molecule is occupied by a total of three water molecules, while for 3 a single molecule of pyridine N- oxide is included and interacts with the host via a strong hydrogen bo nd to a protonated sulfonate substituent. The behavior of 1b as a liga nd for a number of lanthanide elements is also reported. Low temperatu re X-ray structural studies reveal that coordination of the Ln(3+) met al ions to the calixarene ligand occurs exclusively via the sulfonato functionalities and not the phenolic oxygen atoms as suggested by Shin kai et al. for the complexation of UO22+ by 1b. In complex 2 the calix arene exists as the heptaanion. In contrast, crystallization from acid ic solution results in complexes 3-8 retaining all their phenolic prot ons. The protonation constants of 1b have been measured in aqueous sol ution: pK(a) = 10.96(8), 7.63(5), and 4.31(1) at 25 degrees C and 0.1 M KNO3.