catena-Poly[[[aqua-(5-nitro-benzene-1,2,3-tricarboxyl-ato-κO)nickel(II)]-di-μ-aqua-[diaqua-sodium]-di-μ-aqua] tetra-hydrate].

In the title complex, {[NaNi(C(9)H(2)NO(8))(H(2)O)(7)]·4H(2)O}(n), the Ni(II) atom has a distorted octa-hedral coordination, defined by five O atoms from five water mol-ecules and one O atom from one 5-nitro-benzene-1,2,3-tricarboxyl-ate ligand. The Na cation is coordinated by six water O atoms in an irregular trigonal-prismatic geometry. There are seven coordinated water mol-ecules in the asymmetic unit. The Ni and Na atoms are linked by water bridges, forming infinite chains, which are connected by strong O-H⋯O hydrogen bonds involving the coordinated and uncoordinated water mol-ecules into a three-dimensional network.