Supramolecular Isomerism and Polymorphism in Dianion Salts of Pyromellitic Acid

Abstract

The X-ray crystal structures of several salts of pyromellitic acid, H 4PMA, have been determined. The structures of the pyridinium, [C 6H 5NH] 2[H 2PMA], 1, 3-methylpyridinium, [3-CH 3C 6H 4NH] 2[H 2PMA], 2a, [3-CH 3C 6H 4NH] 2-[H 2PMA]·[3-CH 3C 6H 4N], 2b, 4-methylpyridinium, [(4-CH 3C 6H 4N) 2H][4-CH 3C 6H 4NH][H 2PMA], 3, 2-ethylpyridinium, [2-CH 3CH 2C 6H 4N] 2[H 2PMA], 4, 2,4,6-trimethylpyridinium, [2,4,6-(CH 3) 3C 6H 4NH] 2[H 2PMA], 5a and 5b, and quinolinium, [C 9H 7NH] 2[H 2PMA], 6, salts were characterized and analyzed in terms of their networking and crystal packing. The structures of 1– 6 reveal the existence of 0D, 1D, 2D, or 3D O-H···O − hydrogen bonded networks that are sustained and controlled by self-assembly of H 2PMA 2− anions. Five structures, 1, 2a, 3, 4, and 6 form 0D complexes, whereas 1D, 2D, and 3D networks occur in 5a, 2b, and 5b, respectively. The relatively high occurrence of the 0D species might be attributable to a greater likelihood that more efficient crystal packing should generally occur in 0D complexes when compared to higher dimensional networks, in which open spaces are more likely. The formation of such a variety of networks by a single tecton, supramolecular isomerism, resembles that which has been observed in coordination polymer networks in which 4,4′-bipyridine or related ligands are used as spacer ligands.