Synthesis and X-ray structures of iodothiacalix[4]arenes

Mono-, di-, and tetraiodothiacalix[4]arenes 13–16 have been successfully synthesized for the first time by the Griess reaction of diazonium salts of the corresponding aminothiacalix[4]arenes 4–7. X-ray crystallography reveals that monoiodinated compound 13 adopts a distorted pinched cone conformation, in which the three hydroxy groups and the iodine atom form a pseudo-cyclic hydrogen bonding. On the other hand, tetraiodinated compound 16 adopts a 1,3-alternate conformation presumably due to the steric hindrance and dipole repulsion between the iodine atoms.