Tetraaqua{5-[(pyridin-2-ylmethylidene)amino]benzene-1,3-dicarboxylato-κ2 N,N′}nickel(II) tetrahydrate

The title structure, [Ni(C14H8N2O4)(H2O)4]·4H2O, contains a mononuclear NiII complex formed by a chelating bidentate Schiff base and by four Ni-bonded water molecules. The NiII atom is in a distorted octahedral coordination by two N atoms in a cis disposition [Ni—N = 2.0753 (16) and 2.1048 (16) Å] and by four water O atoms [Ni—O = 2.0500 (15)–2.0822 (15) Å]. The crystal structure is completed by four further non-coordinating water molecules and all constituents are linked in a three-dimensional manner by an extensive system of 16 O—H⋯O hydrogen bonds.

The title structure, [Ni(C 14

sup-1
Acta Cryst. Schiff bases with carboxylic groups derived from pyridine 2-carboxaldehyde and amino carboxylic acids are a kind of multifunctional ligand having several potential coordination sites involving N and carboxylate oxygen atoms. The structural chemistry of the coordination compounds of Schiff bases involving some amino benzoic acids and amino acids have been studied (Buffin et al., 2004;Datta et al., 2005;Jiang et al., 2007). However, that of 5-(pyridin-2-ylmethyleneamino)isophthalic acid created by condensation of pyridine 2-carboxaldehyde and 5-aminoisophthalic acid has not been reported. Herein, we describe the synthesis and structural characterization of a new nickel complex coordinated by 5-(pyridin-2-ylmethyleneamino)isophthalic acid. The structure is built up from a neutral mononuclear complex  (Table 1). They link the constituents into a three-dimensional supramolecular structure.
Nine of these hydrogen bonds are accepted by carboxyl oxygen atoms, while seven are accepted by the water molecules (with one exception by non-coordinating water molecules, cf. Table 1).

Experimental
The title complex was prepared by slowly adding 1 ml of H 2 O solution of 5-(pyridin-2-ylmethyleneamino)isophthalic acid (0.1 mmol, 27.1 mg) to 6 ml of a solution of Ni(NO 3 ) 2 (0.1 mmol, 18.2 mg) in MeOH/H 2 O (V:V = 2:1) at room temperature with stirring. The pH value of the solution was adjusted to 7 by addition of aqueous NaOH. The resulting solution was slowly evaporated at room temperature over several days until green single crystals suitable for X-ray diffraction were obtained.

Refinement
All C-bound H atoms were placed geometrically and treated as riding with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). The water H atoms were located in a difference Fourier map and refined in x,y,z and U iso (H) using an distance restraint of O-

Figure 1
Molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level for nonhydrogen atoms, hydrogen atoms are shown as small circles of arbitrary radius.

Tetraaqua{5-[(pyridin-2-ylmethylidene)amino]benzene-1,3-dicarboxylato-κ 2 N,N′}nickel(II) tetrahydrate
Crystal data [Ni(C 14 (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.