1,10-Phenanthrolin-1-ium hydrogen d,l-tartrate dihydrate

In the title hydrated molecular salt, C(12)H(9)N(2) (+)·C(4)H(5)O(6) (-)·2H(2)O, the cation is almost planar (r.m.s. deviation = 0.014 Å); the carbon skeleton of the anion assumes a trans conformation [C-C-C-C torsion angle = -179.86 (14)°]. The carboxyl end of one hydrogen tartrate anion forms a short hydrogen bond to the carboxyl-ate end of another anion [O⋯O = 2.508 (2) Å] in a head-to-tail manner, forming a chain; the chains and water mol-ecules inter-act, generating an O-H⋯O hydrogen-bonded layer. The cation binds to the layer by an N-H⋯O hydrogen bond.