Diaquabis[4-(4H-1,2,4-triazol-4-yl)benzoato-κ2 O,O′]nickel(II)

In the title compound, [Ni(C9H6N3O2)2(H2O)2], the NiII atom lies on a twofold rotation axis and is six-coordinated by two bidentate chelating 4-(1,2,4-triazol-4-yl)benzoate ligands and two water molecules in a distorted octahedral geometry. Intermolecular O—H⋯N hydrogen bonds link the complex molecules into a two-dimensional network parallel to (010).

In the title compound, [Ni(C 9 H 6 N 3 O 2 ) 2 (H 2 O) 2 ], the Ni II atom lies on a twofold rotation axis and is six-coordinated by two bidentate chelating 4-(1,2,4-triazol-4-yl)benzoate ligands and two water molecules in a distorted octahedral geometry. Intermolecular O-HÁ Á ÁN hydrogen bonds link the complex molecules into a two-dimensional network parallel to (010).

Comment
The construction of novel coordination complexes is the current interest in the field of supramolecular chemistry and crystal engineering stemming from their potential applications as functional materials, as well as their intriguing variety of architectures and topologies (Perry et al., 2004;Qin et al., 2005). Heterocyclic carboxylates have often been used as mono-, bi-or multi-dentate ligands to bind transition metal centers, leading to the formation of moderately robust metal-organic coordination frameworks (Mahata et al., 2009;Shi et al., 2009). In this contribution, we selected 4-(1,2,4-triazol-4-yl)benzoic acid (Htyb) as an organic carboxylate ligand, generating the title compound, which is reported here.
In the title compound, the Ni II atom lies on a twofold rotation axis and adopts a distorted octahedral coordination geometry, being coordinated by four carboxylate O atoms from two tyb ligands and two water molecules ( Fig. 1, Table 1). The Ni-O bond lengths and the O-Ni-O bond angles are in the normal range (Zhu, 2010). Intermolecular O-H···N hydrogen bonds (Table 2) stabilize the structure and give a two-dimensional network (Fig. 2).

Experimental
The synthesis was performed under hydrothermal conditions. A mixture of Ni(CH 3 COO) 2 .4H 2 O (0.2 mmol, 0.05 g), 4-(1,2,4-triazol-4-yl)benzoic acid (0.4 mmol, 0.075 g), NaOH (0.4 mmol, 0.016 g) and H 2 O (15 ml) in a 25 ml stainless steel reactor with a Teflon liner was heated from 293 to 443 K in 2 h and a constant temperature was maintained at 443 K for 72 h. After the mixture was cooled to 298 K, green crystals of the title compound were obtained.

Refinement
H atoms on C atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 Å and with U iso (H) = 1.2U eq (C). H atoms bonded to water O atom were located in a difference Fourier map and refined with a restraint of O-H = 0.85 (1) Å.