Bis[8-ethyl-5-oxo-2-(piperazin-4-ium-1-yl)-5,8-dihydro-pyrido[2,3-d]pyrimidine-6-carb-oxy-lic acid] 2,5-dicarb-oxy-benzene-1,4-di-carboxyl-ate octa-hydrate.

The asymmetric unit of the title compound, 2C(14)H(18)N(5)O(3) (+)·C(10)H(5)O(8) (2-)·8H(2)O, contains one [H(2)ppa](+)cation, one half of an [H(2)btec](2-) anion (H(4)btec = 1,2,4,5-benzene-tetra-carb-oxy-lic acid and Hppa = 8-ethyl-5-oxo-2-piperazin-1-yl-5,8-dihydro-pyrido[2,3-d]pyrimidine-6-carb-oxy-lic acid) that is completed by inversion symmetry and four water mol-ecules. In the crystal, the mol-ecules are connected by inter-molecular hydrogen-bonding inter-actions and π-π stacking between the benzene rings of the [H(2)btec](2-) anion and the pyrimidine rings of the [H(2)ppa](+) cation [centroid-centroid distance = 3.597†(3)†à ], generating a three-dimensional supra-molecular structure.