Crystal structure of bis[(5-amino-1H-1,2,4-triazol-3-yl-κN 4)acetato-κO]diaquanickel(II) dihydrate

The title compound, bis[(5-amino-1H-1,2,4-triazol-3-yl-κN 4)acetato-κO]diaqua)nickel(II) dihydrate, is the first transition metal complex of 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA).

In a continuation of our work on the synthesis and reactivity of aminotriazole carboxylic acids (Chernyshev et al., 2006(Chernyshev et al., , 2009(Chernyshev et al., , 2010, we have focused our attention on another chelating ligand, namely 2-(5-amino-1H-1,2,4-triazol-3yl)acetic acid (ATAA, Fig. 1), which can be considered as a homologue of ATCA. To the best of our knowledge, ATAA or its derivatives have not been studied previously for the synthesis of coordination compounds. Herein, we report the synthesis and crystal structure of an Ni II complex of ATAA, the title compound [Ni(C 4

Supramolecular features
In the crystal, molecules of the complex and lattice water molecules are linked into a three-dimensional framework by extensive N-HÁ Á ÁO, O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds (Table 1, Fig. 3).

Figure 2
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Intramolecular N-HÁ Á ÁO hydrogen bonds are shown as dashed lines. Equivalent atoms are generated by symmetry code Àx, Ày, Àz.

Synthesis and crystallization
All attempts to prepare crystals of complex (1) suitable for X-ray investigation by mixing solutions of ATAA or its sodium salt with solutions of Ni II salts were unsuccessful and only microcrystalline precipitates of the sparingly soluble complex were obtained. Crystals of acceptable quality were prepared by slow hydrolysis of ethyl 2-(5-amino-1H-1,2,4triazol-3-yl)acetate (2) in an aqueous solution of nickel nitrate (Fig. 4). A solution of 0.65 g (3.8 mmol) of compound (2) in water (10 ml) was added to a solution of 0.55 g, (1.9 mmol) of Ni(NO 3 ) 2 Á6H 2 O in water (5 ml). After standing at room temperature for two weeks, the formed crystals were collected by filtration yielding the target compound (1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2   program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012). Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.  (14) 0.0280 (11) −0.0022 (11) 0.0007 (9) 0.0026 (11) Geometric parameters (Å, º)