title: Bis(melaminium) tartrate dihydrate.
abstract: In the title compound, 2C(3)H(7)N(6) (+)·C(4)H(4)O(6) (2-)·2H(2)O, in which the complete anion is generated by crystallographic twofold symmetry, there are O-H⋯O, N-H⋯O and N-H⋯N hydrogen-bonding inter-actions between neighbouring moieties, forming layers parallel to the bc plane. In addition, π-π contacts [centroid-centroid distance = 3.6541 (9) Å] between the six-membered rings of the melamine cations are observed.
authors.affiliation: Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang 321004, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Su
authors.forename: Yao-Kang
authors.initials: YK
authors.lastname: Lv
authors.forename: Yun-Long
authors.initials: YL
authors.lastname: Feng