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 carboxyl­ate end of another anion [O⋯O = 2.508 (2) Å] in a head-to-tail manner, forming a chain; the chains and water mol­ecules inter­act, generating an O—H⋯O hydrogen-bonded layer. The cation binds to the layer by an N—H⋯O hydrogen bond.