Benzene-1,2,4,5-tetracarboxylicacidbis(1,3,7-trimethyl- 2,3,6,7-tetrahydro1H- purine-2,6-dione)

The asymmetric unit of the title co-crystal, C10H6O8 center dot 2C(8)H(10)N(4)O(2), comprises a centrosymmetric benzene-1,2,4,5-tetracarboxylic acid (LH4) molecule and a molecule of caffeine in a general position. LH4 is nonplanar, with the dihedral angles between the ring and pendent carboxylic acid groups being 44.22 (7) and 49.74 (7)degrees. By contrast, the caffeine molecule is planar (r.m.s. deviation = 0.040 A degrees). Supramolecular layers parallel to (110) are sustained by carboxylic acid O-H center dot center dot center dot O(carbonyl) and O-H center dot center dot center dot N(imidazole) hydrogen bonds, as well as by methyl-carbonyl C-H center dot center dot center dot O interactions. These stack via pi-pi interactions between the benzene and imidazole rings [inter-centroid distance = 3.4503 (10) angstrom].