One-dimensional hydrogen-bonded structures in the 1:1 proton-transfer compounds of 4,5-dichlorophthalic acid with 8-hydroxyquinoline, 8-aminoquinoline and quinoline-2-carboxylic acid (quinaldic acid).

The structures of the 1:1 proton-transfer compounds of 4,5-dichlorophthalic acid with 8-hydroxyquinoline, 8-aminoquinoline and quinoline-2-carboxylic acid (quinaldic acid), namely anhydrous 8-hydroxyquinolinium 2-carboxy-4,5-dichlorobenzoate, C(9)H(8)NO(+) x C(8)H(3)Cl(2)O(4)(-), (I), 8-aminoquinolinium 2-carboxy-4,5-dichlorobenzoate, C(9)H(9)N(2)(+) x C(8)H(3)Cl(2)O(4)(-), (II), and the adduct hydrate 2-carboxyquinolinium 2-carboxy-4,5-dichlorobenzoate quinolinium-2-carboxylate monohydrate, C(10)H(8)NO(2)(+) x C(8)H(3)Cl(2)O(4)(-) x C(10)H(7)NO(2) x H(2)O, (III), have been determined at 130 K. Compounds (I) and (II) are isomorphous and all three compounds have one-dimensional hydrogen-bonded chain structures, formed in (I) through O-H...O(carboxyl) extensions and in (II) through N(+)-H...O(carboxyl) extensions of cation-anion pairs. In (III), a hydrogen-bonded cyclic R(2)(2)(10) pseudo-dimer unit comprising a protonated quinaldic acid cation and a zwitterionic quinaldic acid adduct molecule is found and is propagated through carboxylic acid O-H...O(carboxyl) and water O-H...O(carboxyl) interactions. In both (I) and (II), there are also cation-anion aromatic ring pi-pi associations. This work further illustrates the utility of both hydrogen phthalate anions and interactive-group-substituted quinoline cations in the formation of low-dimensional hydrogen-bonded structures.