Bis{4-[(Z)-N′-(4-hydroxy­benzyl­idene)hydrazino]-8-(trifluoro­meth­yl)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 mol­ecules (Z′ = 2). The dihedral angle between the mean planes of the 4-hydroxy­phenyl 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 inter­molecular O—H⋯O and N—H⋯O hydrogen bonding between H atoms from 4-hydroxy­phenyl 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-hydroxy­phenyl and quinolinium rings parallel to the (011) plane. There is also an extensive array of inter­molecular hydrogen bonds between water mol­ecules themselves and with sulfate O atoms, as well as hydrogen-bond inter­actions between H atoms from the hydrazino group and sulfate O atoms. In addition, inter­molecular π–π stacking inter­actions occur between nearby 4-hydroxy­phenyl and quinolinium groups, with distances between the centroids of inter­acting rings in the range 3.4140 (9)–3.9659 (9) Å.