Cytosinium orotate dihydrate

The title compound, C4H6N3O+·C5H3N2O4 ·2H2O or Cyt+·Or ·2H2O, 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 R22(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 R22(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 R32(8) and R32(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)°.