Calix[4]arene dimers; Self-assembly via hydrogen bonding at the upper rim

The X-ray structure determination of calix[4]arenedicarboxylic acid unequivocally proves the self-assembled dimeric structure in the solid state, Also in apolar solvents two calix[4]arene molecules are connected via carboxylic acid moieties at the upper rim, NMR studies show that in polar solvents the calix[4]arenedicarboxylic acid is present as a monomer with a pinched cone conformation that differs from the dimeric structure in apolar solvents.