Cytosinium orotate dihydrate

The title compound, C(4)H(6)N(3)O(+)·C(5)H(3)N(2)O(4) (−)·2H(2)O or Cyt(+)·Or(−)·2H(2)O, was synthesized by a reaction between cytosine (4-amino-2-hy­droxy­pyrimidine, Cyt) and orotic acid (2,4-dihy­droxy-6-carb­oxy­pyrimidine, Or) in aqueous solution. The two ions are joined by two N(+)—H⋯O(−) (±)-(CAHB) hydrogen bonds, forming a dimer with graph-set motif R (2) (2)(8). In the crystal, the ion pairs of the asymmetric unit are joined by four N—H⋯O inter­actions to adjacent dimers, forming hydrogen-bonded rings with R (2) (2)(8) graph-set motif in a two-dimensional network. The formation of the three-dimensional array is facilitated by water mol­ecules, which act as bridges between structural sub-units linked in R (3) (2)(8) and R (3) (2)(7) hydrogen-bonded rings. The orotate anion is essentially planar, as the dihedral angle between the planes defined by the carboxylate group and the uracil fragment is 4.0 (4)°.