SUPRAMOLECULAR ISOMERISM AND POLYMORPHISM IN DIANION SALTS OF PYROMELLITIC ACID

The X-ray crystal structures of several salts of pyromellitic acid, H( 4)PMA, have been determined. The structures of the pyridinium, [C6H5NH ](2)[H(2)PMA], 1,3-methylpyridinium, [3-CH3C6H4NH](2)[H(2)PMA], 2a, [3 -CH3C6H4NH](2)-[H(2)PMA]. [3-CH3C6H4N], 2b, 4-methylpyridinium, [(4-CH 3C6H4N)(2)H][4-CH3C6H4NH][H(2)PMA, 3,2-ethylpyridinium, [2-CH3CH2C6H4N ](2)[H(2)PMA], 4, 2,4,6-trimethylpyridinium, [2,4,6-(CH3)(3)C6H4NH](2) [H(2)PMA], 5a and 5b, and quinolinium, [C9H7NH](2)[H(2)PMA], 6, salts were characterized and analyzed in terms of their networking and cryst al 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 contr olled by self-assembly of H(2)PMA(2-) anions. Five structures, 1, 2a, 3, 4, and 6 form 0D complexes, whereas 1D, 2D, and 3D networks occur i n 5a, 2b, and 5b, respectively. The relatively high occurrence of the 0D species might be attributable to a greater likelihood that more eff icient crystal packing should generally occur in 0D complexes when com pared to higher dimensional networks, in which open spaces are more li kely. The formation of such a variety of networks by a single tecton, supramolecular isomerism, resembles that which has been observed in co ordination polymer networks in which 4,4'-bipyridine or related Ligand s are used as spacer ligands. (C) 1998 Elsevier Science Ltd.