Bis{4-[(Z)-N'-(4-hydroxy-benzyl-idene)hydrazino]-8-(trifluoro-meth-yl)quinolinium} sulfate dihydrate.

The title compound, 2C(17)H(13)F(3)N(3)O(+)·SO(4) (2-)·2H(2)O, crystallizes with four independent cations (A, B, C and D) in the asymmetric unit, which is composed of two groups of two cations, one anion and two water mol-ecules (Z' = 2). The dihedral angle between the mean planes of the 4-hydroxy-phenyl and quinolinium groups is 8.9†(7)° in A, 30.1†(6)° in B, 28.8†(8)° in C and 12.8†(1)° in D. The crystal packing is stabilized by inter-molecular O-H⋯O and N-H⋯O hydrogen bonding between H atoms from 4-hydroxy-phenyl O atoms and the O atoms of nearby water molecules and sulfate anions, as well as H atoms from the N atom of the hydrazino group to O atoms of neighboring sulfate anions, linking the components into chains with the 4-hydroxy-phenyl and quinolinium rings parallel to the (011) plane. There is also an extensive array of inter-molecular hydrogen bonds between water mol-ecules themselves and with sulfate O atoms, as well as hydrogen-bond inter-actions between H atoms from the hydrazino group and sulfate O atoms. In addition, inter-molecular π-π stacking inter-actions occur between nearby 4-hydroxy-phenyl and quinolinium groups, with distances between the centroids of inter-acting rings in the range 3.4140†(9)-3.9659†(9)†à .