Mellitate anions: unique anionic component with supramolecular self-organizing properties

Abstract

Mellitate obtained by deprotonation of mellitic acid (benzene hexacarboxylic acid) is a unique anion; the negative charge and the hydrogen-bonding network pattern in the crystal structure vary with the number of sites deprotonated. Structural studies on a number of organic ammonium salts have revealed that the formation of an infinite network of mellitate anions occurs preferentially even in conditions in which proton donors co-exist in solution. The advantage of utilizing mellitate as an anionic component is that the cationic component is packed in the space provided by the anionic network. This scheme can be applied even when attractive forces, such as π–π stacking of π-radicals, operate between the cations. The combination with mellitate has been determined to lead to novel assembly structures of such cationic species.