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

The title compound, [Ni(C(4)H(5)N(4)O(2))(2)(H(2)O)(2)]·2H(2)O, represents the first transition metal complex of the novel chelating triazole ligand, 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA), to be structurally characterized. In the mol­ecule of the title complex, the nickel(II) cation is located on an inversion centre and is coordinated by two water mol­ecules in axial positions and two O and two N atoms from two trans-oriented chelating anions of the deprotonated ATAA ligand, forming a slightly distorted octa­hedron. The trans angles of the octa­hedron are all 180° due to the inversion symmetry of the mol­ecule. The cis-angles are in the range 87.25 (8)–92.75 (8)°. The six-membered chelate ring adopts a slightly twisted boat conformation with puckering parameters Q = 0.542 (2) Å, Θ = 88.5 (2) and ϕ = 15.4 (3)°. The mol­ecular conformation is stabilized by intra­molecular N—H⋯O hydrogen bonds between the amino group and the chelating carboxyl­ate O atom of two trans-oriented ligands. In the crystal, the complex mol­ecules and lattice water mol­ecules are linked into a three-dimensional framework by an extensive network of N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds.