The structures of the anhydrous 1:1 proton-transfer compounds of 4,5-dichlorophthalic acid (DCPA) with the monocyclic heteroaromatic Lewis bases 2-aminopyrimidine, 3-(aminocarbonyl)pyridine (nicotinamide) and 4-(aminocarbonyl)pyridine (isonicotinamide), namely 2-aminopyrimidinium 2-carboxy-4,5-dichlorobenzoate, C4H6N3+烸H3Cl2O4-, (I), 3-(aminocarbonyl)pyridinium 2-carboxy-4,5-dichlorobenzoate, C6H7N2O+烸H3Cl2O4-, (II), and the unusual salt adduct 4-(aminocarbonyl)pyridinium 2-carboxy-4,5-dichlorobenzoate-methyl 2-carboxy-4,5-dichlorobenzoate (1/1), C6H7N2O+烸H3Cl2O4-烹H6Cl2O4, (III), have been determined at 130 K. Compound (I) forms discrete centrosymmetric hydrogen-bonded cyclic bis(cation-anion) units having both R22(8) and R12(4) N-HO interactions. In (II), the primary N-HO-linked cation-anion units are extended into a two-dimensional sheet structure via amide-carboxyl and amide-carbonyl N-HO interactions. The structure of (III) reveals the presence of an unusual and unexpected self-synthesized methyl monoester of the acid as an adduct molecule, giving one-dimensional hydrogen-bonded chains. In all three structures, the hydrogen phthalate anions are essentially planar with short intramolecular carboxyl-carboxylate O-HO hydrogen bonds [OO = 2.393 (8)-2.410 (2) ŝ. This work provides examples of low-dimensional 1:1 hydrogen-bonded DCPA structure types, and includes the first example of a discrete cyclic `heterotetramer.' This low dimensionality in the structures of the 1:1 aromatic Lewis base salts of the parent acid is generally associated with the planar DCPA anion species.