4-[2-(4-Pyridyl)­ethyl]­pyridinium nitrate trihydrate

The title compound, C12H13N2+·NO3−·3H2O [where C12H13N2+ is the monoprotonated form of 1,2-bis(4-pyridyl)­ethane (BPEH+)] is monoclinic, space group P21/c, and contains two empirical formulae in the asymmetric unit. The compound has cationic [BPEH]nn+ organic layers, alternating in the b direction with anionic [(NO3)·3H2O]nn− inorganic layers. Hydro­gen bonds between 4-pyridyl and 4-pyridinium groups, and between nitrate ions and water mol­ecules, give rise to chains and two-dimensional hydrogen-bonding networks, respectively.