LOWER RIM UPPER RIM HYDROGEN-BONDED ADDUCTS OF CALIX[4]ARENES

An upper-rim-substituted calix[4]arene tetracarboxylic acid forms hydr ogen-bonded duplexes with lower-rim-substituted tetra(4-pyridyl)- and tetra(3-pyridyl)calix[4] arenes in chloroform. The formation of these adducts was studied by extraction experiments. The association constan ts determined via H-1 NMR dilution experiments in CDCl3 are 7.6 x 10(3 ) and 1.3 x 10(3) M(-1) for the 4-pyridyl and the 3-pyridyl derivative , respectively. IR studies in the solid state and in solution indicate that the interaction is based on hydrogen bonding and that the degree of proton transfer is negligible. VPO measurements support the format ion of 1:1 adducts.