Tetraaquabis(3,5-di-4-pyridyl-1,2,4-triazolato-κN)nickel(II) dihydrate

The NiII atom in the title compound, [Ni(C12H8N5)2(H2O)4]·2H2O, lies on a center of inversion and is coordinated by the N atoms of two 3,5-di-4-pyridine-1,2,4-triazolate ligands and by four water O atoms in a slightly distorted octahedral geometry. The coordinated and uncoordinated water molecules interact with the N-heterocycles through O—H⋯N and O—H⋯O hydrogen bonds, generating a three-dimensional supramolecular architecture.

The Ni II atom in the title compound, [Ni(C 12 H 8 N 5 ) 2 (H 2 O) 4 ]Á-2H 2 O, lies on a center of inversion and is coordinated by the N atoms of two 3,5-di-4-pyridine-1,2,4-triazolate ligands and by four water O atoms in a slightly distorted octahedral geometry. The coordinated and uncoordinated water molecules interact with the N-heterocycles through O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen bonds, generating a three-dimensional supramolecular architecture.

Experimental
Crystal data [Ni(C 12

Comment
Transition metal complexes with 1,2,4-triazole derivatives as ligands are of great interest as they are the subject of magnetic studies (Haasnoot, 2000). The ligand 3,5-di(4-pyridine)-1,2,4-triazole is of special interest as it contains multi-dentate donor atoms and shows diverse coordination modes. Especially only a few examples about the coordinaiton chemistry of L are reported. Some unusual coordination modes of L also have been reported forming interesting supramolecular isomerism systems (Zhang et al., 2006).
In this work, we synthesized a new compound [Ni(L) 2 (H 2 O) 4 ](H 2 O) 2 (L = 3,5-di(4-pyridine)-1,2,4-triazolate anions), which is composed of one nickel(II) cation, two L ligand, four coordinated and two lattice water molecules. The nickel(II) cation is six-coordinated in the octahedral geometry. The equatorial site of nickel cation is occupied by four aqua molecules while the axial site is occupied by two nitrogen atoms of two mono-dentate L ligands. The mono-dentate coordination mode of L is different from previously reported di-, tri-or tetra-dentate coordination modes of L (Zhang et al., 2005;Zhang et al., 2006).

O3 acts as both a hydrogen bond donor and a hydrogen bond acceptor. Strong O-H···N and O-H···O hydrogen bonds
generated from water molecules and nitrogen atoms of pyridine or triazole groups are also observed resulting in the threedimensional supramolecular network.

Refinement
All H atoms were found on difference maps. The water H atoms were refined freely, giving an O-H = 0.82-0.86 Å. The remaining H atoms were placed in calculated positions, with C-H = 0.93 Å, and included in the final cycles of refinement using a riding model, with U iso (H) = 1.2U eq (C) Figures   Fig. 1