Aqua(2,2′-bipyridyl)(pyrazine-2,6-dicarboxylato)nickel(II) 1.25-hydrate

The asymmetric unit of the title compound, [Ni(C6H2N2O4)(C10H8N2)(H2O)]·1.25H2O, contains two independent chemically identical NiII complex cations and two and a half solvent water molecules. The NiII ions are in slightly distorted coordination environments. In the crystal structure, intermolecular O—H⋯O and weak C—H⋯O hydrogen bonds link cations and water molecules into a three-dimensional network. One of the three uncoordinated water molecules is half-occupied.

The asymmetric unit of the title compound, [Ni(C 6 H 2 N 2 O 4 )-(C 10 H 8 N 2 )(H 2 O)]Á1.25H 2 O, contains two independent chemically identical Ni II complex cations and two and a half solvent water molecules. The Ni II ions are in slightly distorted coordination environments. In the crystal structure, intermolecular O-HÁ Á ÁO and weak C-HÁ Á ÁO hydrogen bonds link cations and water molecules into a three-dimensional network. One of the three uncoordinated water molecules is half-occupied.

Comment
In general, bridging multifunctional organic ligands with N-and O-donors have been proven to be good candidates as versatile coordination sites and as hydrogen-bond acceptors and donors. Pyrazine-2,6-dicarboxylic acid (H 2 PZDC) has two carboxylic groups and two pyrazine nitrogen atoms, and can be used as hydrogen-bond acceptor as well as hydrogen-bond donor, which assists in the generation of supramolecular structures. Because of the structural character, we have used this ligand in our previous work to construct 3d, 4f and 3d-4f complexes (Wang et al., 2006;Wang, Weng, et al., 2007;Wang, Zheng & Jin, 2007;Wang, Zheng, et al., 2007;Wang, Zheng et al., 2008;Wang, Mu et al., 2008). Generally, when coordinated to transition metal ions, PZDC adopts tridentate (ONO) mode and is involved in various hydrogen-bonding interactions.
In a continuation of our work, we report synthesis and structure of the title complex.
The asymmetric unit of the title compound is shown in Fig. 1. In the crystal structure, intermolecular O-H···O ( Fig. 2) and weak C-H···O hydrogen bonds link cations and water molecules into a three-dimensional network.

Refinement
All water H atoms were found in difference Fourier maps and were fixed during refinement at O-H distances of 0.85-0.86 Cell parameters from 5479 reflections a = 10.7616 (12)