Tetraaquabis(pyridine-κN)nickel(II) dinitrate

In the title compound, [Ni(C5H5N)2(H2O)4](NO3)2, the NiII ion is coordinated by two N-bonded pyridine ligands and four water molecules in an octahedral coordination mode. The asymmetric unit consists of one NiII ion located on an inversion center, as well as one pyridine ligand, one nitrate anion and two water molecules in general positions. In the crystal structure, the discrete complex cations and nitrate anions are connected by O—H⋯O and C—H⋯O hydrogen bonds.

In the title compound, [Ni(C 5 H 5 N) 2 (H 2 O) 4 ](NO 3 ) 2 , the Ni II ion is coordinated by two N-bonded pyridine ligands and four water molecules in an octahedral coordination mode. The asymmetric unit consists of one Ni II ion located on an inversion center, as well as one pyridine ligand, one nitrate anion and two water molecules in general positions. In the crystal structure, the discrete complex cations and nitrate anions are connected by O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds.

Related literature
For general background to thermal decomposition reactions as an alternative tool for the discovery and preparation of new ligand-deficient coordination polymers with defined magnetic properties, see: Wriedt & Nä ther (2009a,b); Wriedt et al. (2009a,b). For a related structure, see: Halut-Desportes (1981).
MW thanks the Stiftung Stipendien-Fonds des Verbandes der Chemischen Industrie and the Studienstiftung des deutschen Volkes for a PhD scholarship. We gratefully acknowledge financial support by the State of Schleswig-Holstein and the Deutsche Forschungsgemeinschaft (Project 720/3-1). We thank Professor Dr Wolfgang Bensch for the opportunity to use his experimental facilities.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HY2315). Recently, we have shown that thermal decomposition reactions are an elegant route for the discovery and preparation of new ligand-deficient coordination polymers with defined magnetic properties (Wriedt & Näther, 2009a,b;Wriedt et al., 2009a,b). In our ongoing investigation on the synthesis, structures and properties of such compounds based on paramagnetic transition metal pseudo-halides and N-donor ligands, we have reacted nickel(II) dinitrate hexahydrate, sodium dicyanamide and pyridine. In this reaction single crystals of the title compound were grown.

Structure Reports Online
The title compound (Fig. 1) represents a discrete complex cation, in which the Ni II atom, lying on an inversion center, is coordinated by two pyridine ligands and four water molecules in an octahedral coordination mode. The nitrate anions are not coordinated to the metal atoms (Fig. 2). The NiN 2 O 4 octahedron is slightly distorted with Ni-N pyridine distances of 2.140 (2) Å and Ni-O water distances of 2.113 (2) and 2.128 (2) Å ( Table 1). The angles arround the metal atoms range between 85.71 (10) to 94.29 (10) and 180°. A similar coordination is found in a related structure (Halut-Desportes, 1981). The opposite pyridyl rings are coplanar due to symmetry. The shortest intermolecular Ni···Ni distance amounts to 7.3245 (4) Å.

Experimental
Ni(NO 3 ) 2 .6H 2 O (72.7 mg, 0.25 mmol), sodium dicyanamide (44.5 mg, 0.5 mmol) and pyridine (0.5 ml) obtained from Alfa Aesar were reacted in a closed test-tube at 120°C for 3 d. On cooling light green block-shaped single crystals of the title compound were grown in a mixture with unknown phases.

Refinement
All H atoms were located in a difference Fourier map. H atoms bound to 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). The water H atoms were disordered over three positions for each water molecule and were refined as riding, with O-H = 0.82 Å and U iso (H) = 1.5U eq (O), using a split model with SOF = 0.6667 for each H atom. sup-2