Received 10 August 2013
The asymmetric unit of the title co-crystal, 2C14H13N2+·C10H4O82-·2C14H12N2·C10H6O8, comprises a 2,9-dimethyl-1,10-phenanthrolin-1-ium cation (Me2PhenH+) and a 2,9-dimethyl-1,10-phenanthroline molecule (Me2Phen), each in a general position, and half each of a 2,5-dicarboxybenzene-1,4-dicarboxylate dianion (LH22-) and a benzene-1,2,4,5-tetracarboxylic acid molecule (LH4), 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  mediated by charge-assisted O-HO- hydrogen bonding between alternating LH4 and LH22-. These are connected to the Me2PhenH+ and Me2Phen species by N-HO and O-HN hydrogen bonds, respectively. A three-dimensional architecture is formed by C-HO and - interactions [inter-centroid distance = 3.5337 (17) Å].
For salt formation with benzene-1,2,4,5-tetracarboxylic acid, see: Arman & Tiekink (2013). For a co-crystal involving 2,9-dimethyl-1,10-phenanthroline, see: Arman et al. (2010). For the structure of a 2,9-dimethyl-1,10-phenanthrolin-1-ium carboxylate salt, see: Derikvand & Olmstead (2011).
Data collection: CrystalClear (Molecular Structure Corporation & Rigaku, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: XU5731 ).
We gratefully thank the Ministry of Higher Education (Malaysia) for funding structural studies through the High-Impact Research scheme (UM.C/HIR-MOHE/SC/03).
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