Low‐dimensional hydrogen‐bonded structures in the 1:1 and 1:2 proton‐transfer compounds of 4,5‐dichlorophthalic acid with the aliphatic Lewis bases triethylamine, diethylamine, n ‐butylamine and piperidine

The structures of the proton‐transfer compounds of 4,5‐dichlorophthalic acid (DCPA) with the aliphatic Lewis bases triethylamine, diethylamine, n ‐butylamine and piperidine, namely triethylaminium 2‐carboxy‐4,5‐dichlorobenzoate, C 6 H 16 N + ·C 8 H 3 Cl 2 O 4 − , (I), diethylaminium 2‐carboxy‐4,5‐dichlorobenzoate, C 4 H 12 N + ·C 8 H 3 Cl 2 O 4 − , (II), bis(butanaminium) 4,5‐dichlorobenzene‐1,2‐dicarboxylate monohydrate, 2C 4 H 12 N + ·C 8 H 2 Cl 2 O 4 2− ·H 2 O, (III), and bis(piperidinium) 4,5‐dichlorobenzene‐1,2‐dicarboxylate monohydrate, 2C 5 H 12 N + ·C 8 H 2 Cl 2 O 4 2− ·H 2 O, (IV), have been determined at 200 K. All compounds have hydrogen‐bonding associations, giving discrete cation–anion units in (I) and linear chains in (II), while (III) and (IV) both have two‐dimensional structures. In (I), a discrete cation–anion unit is formed through an asymmetric R 1 2 (4) N + —H...O 2 hydrogen‐bonding association, whereas in (II), chains are formed through linear N—H...O associations involving both aminium H‐atom donors. In compounds (III) and (IV), the primary N—H...O‐linked cation–anion units are extended into a two‐dimensional sheet structure via amide–carboxyl N—H...O and amide–carbonyl N—H...O interactions. In the 1:1 salts (I) and (II), the hydrogen 4,5‐dichlorophthalate anions are essentially planar with short intramolecular carboxyl–carboxyl O—H...O hydrogen bonds [O...O = 2.4223 (14) and 2.388 (2) Å, respectively]. This work provides a further example of the uncommon zero‐dimensional hydrogen‐bonded DCPA–Lewis base salt and the one‐dimensional chain structure type, while even with the hydrate structures of the 1:2 salts with the primary and secondary amines, the low dimensionality generally associated with 1:1 DCPA salts is also found.