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)

Abstract

The structures of the 1:1 proton-transfer compounds
of 4,5-dichlorophthalic acid with 8-hydroxyquinoline,
8-aminoqunoline and with quinoline-2-carboxylic acid
(quinaldic acid), namely anhydrous
8-hydroxyquinolinium 2-carboxy-4,5-dichlorobenzoate
C~9~H~8~NO^+^ ^.^ C~8~H~3~Cl~2~O~4~^-^ (I) and
8-aminoquinolinium 2-carboxy-4,5-dichlorobenzoate
C~9~H~9~N~2~^+^ ^.^ 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~^+^ ^.^ C~8~H~3~Cl~2~O~4~^-^ ^.^ C~10~H~7~NO~2~ ^.^
H~2~O (III) have been determined at 130 K. Compounds (I) and (II)
are isomorphous and all compounds have one-dimensional
hydrogen-bonded chain structures, 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 a 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 the interactive-group-substituted quinoline
cations in formation of low-dimensional hydrogen-bonded structures.