Crystal structures of two 1:2 dihydrate compounds of chloranilic acid with 2-carb­oxy­pyridine and 2-carb­oxy­quinoline

The crystal structure of the 1:2 dihydrate compound of chloranilic acid (systematic name: 2,5-di­chloro-3,6-dihy­droxy-1,4-benzo­quinone) with 2-carb­oxy­pyridine (another common name: picolinic acid; systematic name: pyridine-2-carb­oxy­lic acid), namely, 2C(6)H(5.5)NO(2) (0.5+)·C(6)HCl(2)O(4) (−)·2H(2)O, (I), has been determined at 180 K, and the structure of the 1:2 dihydrate compound of chloranilic acid with 2-carb­oxy­quinoline (another common name: quinaldic acid; systematic name: quinoline-2-carb­oxy­lic acid), namely, 2C(10)H(7)NO(2)·C(6)H(2)Cl(2)O(4)·2H(2)O, (II), has been redetermined at 200 K. This determination presents a higher precision crystal structure than the previously published structure [Marfo-Owusu & Thompson (2014 ▸). X-ray Struct. Anal. Online, 30, 55–56]. Compound (I) was analysed as a disordered structure over two states, viz. salt and co-crystal. The salt is bis­(2-carb­oxy­pyridinium) chloranilate dihydrate, 2C(6)H(6)NO(2) (+)·C(6)Cl(2)O(4) (2−)·2H(2)O, and the co-crystal is bis­(pyridinium-2-carboxyl­ate) chloranilic acid dihydrate, 2C(6)H(5)NO(2)·C(6)H(2)Cl(2)O(4)·2H(2)O, including zwitterionic 2-carb­oxy­pyridine. In both salt and co-crystal, the water mol­ecule links the chloranilic acid and 2-carb­oxy­pyridine mol­ecules through O—H⋯O and N—H⋯O hydrogen bonds. The 2-carb­oxy­pyridine mol­ecules are connected into a head-to-head inversion dimer by a short O—H⋯O hydrogen bond, in which the H atom is disordered over two positions. Compound (II) is a 1:2 dihydrate co-crystal of chloranilic acid and zwitterionic 2-carb­oxy­quinoline. The water mol­ecule links the chloranilic acid and 2-carb­oxy­quinoline mol­ecules through O—H⋯O hydrogen bonds. The 2-carb­oxy­quinoline mol­ecules are connected into a head-to-tail inversion dimer by a pair of N—H⋯O hydrogen bonds.