3,3-Bis(2-imidazolyl)propionic Acid Hemihydrate

Slow evaporation of an aqueous solution of 3,3-Bis(2-imidazolyl)propionic acid monohydrate, C₉H₁₀N₄O₂.H₂O, yields crystals of the hemihydrate, C₉H₁₀N₄O₂.0.5H₂O. In both hydrates the molecules of 3,3-bis(2-imidazolyl)propionic acid are in a zwitterionic form containing -COO^- and -(imidazole)H⁺ residues, i.e. 3-(2-imidazolyl)-3-(2-imidazolio)propionate. The crystal structure of the hemihydrate contains two crystallographically independent zwitterions and one water molecule linked by hydrogen bonds. In the two molecules of the hemihydrate as well as in the monohydrate, the dihedral angles between the planes of the imidazole rings and of the carboxylate group show remarkable differences indicating that 3,3-bis(2-imidazolyl)propionic acid can be used as a flexible ligand.