Bis(2,9-dimethyl-1,10-phenanthrolin-1-ium) 2,5-di­carb­oxy­benzene-1,4-di­carb­oxyl­ate–2,9-dimethyl-1,10-phenanthroline–benzene-1,2,4,5-tetra­carb­oxy­lic acid (1/2/1)

The asymmetric unit of the title co-crystal, 2C(14)H(13)N(2) (+)·C(10)H(4)O(8) (2−)·2C(14)H(12)N(2)·C(10)H(6)O(8), comprises a 2,9-dimethyl-1,10-phenanthrolin-1-ium cation (Me(2)PhenH(+)) and a 2,9-dimethyl-1,10-phenanthroline mol­ecule (Me(2)Phen), each in a general position, and half each of a 2,5-di­carb­oxy­benzene-1,4-di­carboxyl­ate dianion (LH(2) (2−)) and a benzene-1,2,4,5-tetra­carb­oxy­lic acid mol­ecule (LH(4)), each being disposed about a centre of inversion. Small twists are evident in the dianion [the C—C—C—O torsion angles are 168.41 (18) and 16.2 (3)°], whereas a major twist is found for one carb­oxy­lic acid group in the neutral mol­ecule [C—C—C—O = 66.3 (2) and 18.2 (3)°]. The most prominent feature of the crystal packing is the formation of linear supra­molecular chains along [001] mediated by charge-assisted O—H⋯O(−) hydrogen bonding between alternating LH(4) and LH(2) (2−). These are connected to the Me(2)PhenH(+) and Me(2)Phen species by N—H⋯O and O—H⋯N hydrogen bonds, respectively. A three-dimensional architecture is formed by C—H⋯O and π–π inter­actions [inter-centroid distance = 3.5337 (17) Å].