Bis[8-ethyl-5-oxo-2-(piperazin-4-ium-1-yl)-5,8-dihydro­pyrido[2,3-d]pyrimidine-6-carb­oxy­lic acid] 2,5-dicarb­oxy­benzene-1,4-di­carboxyl­ate octa­hydrate

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-benzene­tetra­carb­oxy­lic acid and Hppa = 8-ethyl-5-oxo-2-piperazin-1-yl-5,8-dihydro­pyrido[2,3-d]pyrimidine-6-carb­oxy­lic acid) that is completed by inversion symmetry and four water mol­ecules. In the crystal, the mol­ecules are connected by inter­molecular hydrogen-bonding inter­actions 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) Å], generating a three-dimensional supra­molecular structure.