catena-Poly[[[aqua(5-nitrobenzene-1,2,3-tricarboxylato-κO 1)nickel(II)]-di-μ-aqua-[diaquasodium]-di-μ-aqua] tetrahydrate]

In the title complex, {[NaNi(C9H2NO8)(H2O)7]·4H2O}n, the NiII atom has a distorted octahedral coordination, defined by five O atoms from five water molecules and one O atom from one 5-nitrobenzene-1,2,3-tricarboxylate ligand. The Na cation is coordinated by six water O atoms in an irregular trigonal-prismatic geometry. There are seven coordinated water molecules 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 molecules into a three-dimensional network.

In the title complex, {[NaNi(C 9 H 2 NO 8 )(H 2 O) 7 ]Á4H 2 O} n , the Ni II atom has a distorted octahedral coordination, defined by five O atoms from five water molecules and one O atom from one 5-nitrobenzene-1,2,3-tricarboxylate ligand. The Na cation is coordinated by six water O atoms in an irregular trigonalprismatic geometry. There are seven coordinated water molecules in the asymmetic unit. The Ni and Na atoms are linked by water bridges, forming infinite chains, which are connected by strong O-HÁ Á ÁO hydrogen bonds involving the coordinated and uncoordinated water molecules into a threedimensional network.

Comment
It is well-known that carboxylate ligands play an important role in coordination chemistry. They usually adopt diverse binding modes as terminal monodentate, chelating to one metal center, bridging to two metal centers (Ding et al., 2010;Li et al., 2006). In the present paper, we synthesized a novel green complex {[NiNa(C 9 H 2 NO 8 )(H 2 O) 7 ].4(H 2 O)} n based on 5-nitrobenzene-1,2,3-tricarboxylate ligand. It is isostructural to the copper compound reported by Ding & Zhao, (2010). The Ni and Na atoms are linked by water bridges, forming an infinite chain (Fig.2). They are arrayed by turns with the distance of 3.4258 (21)Å and 3.7373 (20)Å between Ni and Na. The chains are connected by strong O-H···O hydrogen bonds involving the coordinated and uncoordinated water molecules into a three-dimensional network (Table 1). In the .4(H 2 O)} n compound, the six Cu-O bond lengths range between 2.028 (2) and 2.098 (3) Å. It is a rare case that all Cu-O distances are above 2.00 Å, which may be explained by the influence of the Na-O-Cu bridges.
But in the title compound, the Ni-O bond lengths range between 2.032 (2) and 2.106 (3) Å and represent normal values.

Experimental
A mixture of 5-nitrobenzene-1,2,3-tricarboxylate ligand (0.1 mmol), Ni(NO 3 ) 2 (0.1 mmol) and H 2 O (20 ml) was treated with a solution of NaOH until the pH about 7-8. and left to stand at room temperature for about a few weeks,then the green crystals were obtained.

Refinement
Carbon bound H atoms were placed at calculated positions and were treated as riding on the parent C atoms with C-H = 0.93 Å, and with U iso (H) = 1.2 U eq (C). The water H-atoms were located in a difference map, and were refined with a distance restraint of O-H = 0.84 Å; their U iso values were refined.  catena-Poly [[[aqua(5-nitrobenzene-1,2,3- Hall symbol: -P 1 Mo Kα radiation, λ = 0.71073 Å a = 6.7005 (6)

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) supplementary materials sup-9