Pseudopolymorph and Infinite Hydrogen Bonding Network of Cyclic Oligomers of m-Aminobenzenesulfonic Acid

A cyclic trimer and a cyclic tetramer of m-aminobenzenesulfonic acid were obtained by one-pot synthesis using dichlorotriphenylphosphorane as a coupling reagent. Single crystal X-ray analysis revealed that all sulfonamide moieties of the cyclic sulfonamides adopted a synclinal conformation, and that multiple intermolecular hydrogen bonds were formed between the sulfonamide protons and the sulfonyl oxygens on the adjacent molecules. The cyclic trimer has three types of pseudopolymorph containing water, methanol, or acetonitrile molecules. The molecule in each crystal was bowl-shaped, and the enantiomeric pair of molecules existed in a discrete dimeric structure with or without a guest molecule in the cavity. Furthermore, the cyclic tetramer existed in a 1,3-alternate conformation with pseudo-S₄-symmetry, and formed an infinite network structure through intermolecular hydrogen bonds.