Bis(2-carb-oxy-N-{[1-(2-hy-droxy-eth-yl)-3,3-dimethyl-indolin-2-yl-idene]methyl-imino}-anilinium) sulfate monohydrate.

The asymmetric unit of the title compound, 2C20H22N3O3(+)·SO4(2-)·H2O, contains four cations, two sulfate anions and two lattice water mol-ecules. One of the four cations shows a different conformation of the hy-droxy-ethyl group; the remaining three are all essentially superimposable. Two cations exhibit two-site orientational disorder [ratios = 0.524 (5):0.476 (5) and 0.616 (6):0.384 (6)] of the last two atoms of their hy-droxy-ethyl groups, and one water mol-ecule is disordered over two positions in a 0.634 (13):0.366 (13) ratio. Each imine H atom is intra-molecularly in contact with the adjacent carboxyl O atom, forming an S(6) motif, while all the carb-oxy-lic acid H atoms are hydrogen bonded to O atoms of the sulfate anions. Other notable hydrogen-bond inter-actions involve (methyl-ene, phenyl and imine chain) C-H⋯O (sulfate and carbox-yl) and O-H⋯O(water) contacts, making up a comprehensive three-dimensional network involving D2(2)(n), with n = 4-6 and 15-16, and C2(2)(17) classical hydrogen-bond motifs. The crystal investigated was twinned by pseudomerohedry with a twin component ratio of 0.4745 (12):0.5255 (12).