Crystal structure of hexa­aqua­nickel(II) bis{2-[(5,6-di­hy­droxy-3-sul­fon­ato­quino­lin-1-ium-7-yl)oxy]acetate} dihydrate

The asymmetric unit of the title compound, [Ni(H(2)O)(6)](C(11)H(8)NO(8)S)(2)·2H(2)O, features a half-hexa­aqua­nickel(II) complex cation with the Ni(II) ion on an inversion center, one deprotonated 5,6-dihy­droxy-3-sulfoquinolin-7-yloxyacetic acid (QOH) molecule appearing in its zwitterionic form and one lattice water mol­ecule. The sulfonate group is disordered over two positions with occupancy factors of 0.655 (5) and 0.345 (5). The hexa­aqua­nickel(II) cation inter­acts through hydrogen bonding with eight QOH mol­ecules and two water mol­ecules. The six-membered rings of quinoline show π–π stacking [centroid-to-centroid distances of 3.679 (2) Å and 3.714 (2) Å].