Bis(acetylacetonato-κ2 O,O′)bis(pyridine-κN)nickel(II) dihydrate

The title compound, [Ni(C5H7O2)2(C5H5N)2]·2H2O, crystallizes with two half-molecules in the asymmetric unit. The NiII ion of each unique complex molecule lies on an inversion centre and has an octahedral coordination geometry. The crystal structure features weak O—H⋯O hydrogen bonds, which form chains running parallel to the a axis.

The title compound, [Ni(C 5 H 7 O 2 ) 2 (C 5 H 5 N) 2 ]Á2H 2 O, crystallizes with two half-molecules in the asymmetric unit. The Ni II ion of each unique complex molecule lies on an inversion centre and has an octahedral coordination geometry. The crystal structure features weak O-HÁ Á ÁO hydrogen bonds, which form chains running parallel to the a axis.

Experimental
Crystal data [Ni(C 5    the title compound, Zukerman-Schpector et al. (2007) published a methyl pyridine derivative, and the 3 and 4-cyanopyridine derivatives were also reported by Zukerman-Schpector and co-workers (2000). Other structures have been obtained with derivatives of acac: 1,3-diphenyl-1,3-propanedionato (Soldatov, et al., (2001)) and 4-pyridyltetrathiafulvalene (Wang, et al., (2006)). All the bond lengths and angles are in the normal range (Elder et al., 1968;Zukerman-Schpector et al., 2000;Wang et al., 2006). The two independent units are linked to each other by weak O-H···O hydrogen bonds (see Table 2 for geometric details) which form a one-dimensional chain, running parallel to a as shown in Fig. 2. Another feature in this crystal structure is the presence of C-H···π interactions, which further stabilize the crystal packing. These C-H···π interactions are present between the C-H group of acac and an adjacent pyridine rings with a H···π distance of 3.183 Å (Fig. 2).

Experimental
An amount of 0.075 g (0.5 mmol) of mercapto succinic acid was dissolved in 2 ml of pyridine and 0,1374 g (0.5 mmol) of nickel(II) acetylacetonate was dissolved in 10 ml methanol. The two solutions were mixed and stirred for 15 min. The resulting solution was allowed to stand at room temperature. After several days X-ray quality blue crystals were obtained.
A fragment cut from a larger crystal was used for data collection.

Refinement
Water hydrogen atoms were tentatively found in the difference density Fourier map and were refined with an isotropic displacement parameter 1.5 that of the adjacent oxygen atom. The O-H distances were restrained to be 0.9 Å within a standard deviation of 0.01 with U iso (H) = 1.5 U eq (O) and the H···H contacts were restraint to 1.40 Å with a standard deviation of 0.02. All other Hydrogen atoms were placed in calculated positions with C-H distances of 0.93-0.96 Å for aromatic H atoms with U iso (H) = 1.2 U eq (C).

Figure 1
View of the title compound with the atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. symmetry code: i = 1 -x,1 -y,1 -z; ii = -x,1 -y,1 -z.

Figure 2
View down c of the crystal packing of the title compound showing the hydrogen bonds and C-H···π interactions as dashed lines.

Bis(acetylacetonato-κ 2 O,O′)bis(pyridine-κN)nickel(II) dihydrate
Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.