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

The title compound, [Ni(C4H5N4O2)2(H2O)2]·2H2O, 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 mol-ecule of the title complex, the nickel(II) cation is located on an inversion centre and is coordinated by two water mol-ecules 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 octa-hedron. The trans angles of the octa-hedron are all 180° due to the inversion symmetry of the mol-ecule. 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 mol-ecular conformation is stabilized by intra-molecular N-H⋯O hydrogen bonds between the amino group and the chelating carboxyl-ate O atom of two trans-oriented ligands. In the crystal, the complex mol-ecules and lattice water mol-ecules are linked into a three-dimensional framework by an extensive network of N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds.