(3,3′-{(1E,1′E)-1,1′-[Ethane-1,2-diylbis(azan-1-yl-1-ylidene-κN)]bis(ethan-1-yl-1-ylidene)}dipyrazine 1-oxide-κN 4)bis(nitrato-κO)nickel(II) monohydrate

In the title complex, [Ni(NO3)2(C14H16N6O2)]·H2O, the NiII atom, lying on a twofold rotation axis, is coordinated by a tetradentate 3,3′-{(1E,1′E)-1,1′-[ethane-1,2-diylbis(azan-1-yl-1-ylidene)]bis(ethan-1-yl-1-ylidene)}dipyrazine 1-oxide ligand and two mutually trans monodentate nitrate anions in a distorted octahedral geometry. The lattice water molecule is located on a twofold rotation axis. The complex molecules are linked by the water molecules through O—H⋯O hydrogen bonds into a chain along [001]. Further C—H⋯O hydrogen bonds lead to the formation of a three-dimensional network.

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008). In the title complex, the Ni II atom, lying on a twofold rotation axis, exhibits a distorted octahedral geometry, defined by four N atoms from the L ligand, occupying the equatorial plane, and two axial O atoms from two monodentate nitrate anions (Fig. 1). The equatorial Ni-N distances [Ni1-N1 = 2.0855 (19) and Ni1-N3 = 2.0183 (19) Å] are in a normal range for this class of compounds and also very similar to those of Ni-N(pyridine) and Ni-N(imine) found in analogue complexes (Banerjee et al., 2004;Padhi & Manivannan, 2007). Hydrogen bonding plays an important role in the formation of the crystal structure (Table 1). The lattice water molecule is located on a twofold rotation axis and connect two symmetry-related complex molecules through O-H···O hydrogen bonds, so forming a chain structure along [001] ( Fig. 2). C-H···O hydrogen bonds lead to a three-dimensional network (Fig. 3).

Experimental
Synthesis of 2-acetylpyrazine-N-oxide: 2-Acetylpyrazine (12.2 g, 0.1 mol), glacial acetic acid (75 ml) and 30% hydrogen peroxide (14 ml) were heated with reflux at 70-80°C for 3 h. Additional 30% H 2 O 2 (10 ml) was added and the temperature was maintained at 70-80°C for a further 10 h. The solvent was removed by rotary evaporation and upon standing brown yellow solid was formed, filtered and dried.
Synthesis of the title complex: Ni(NO 3 ) 2 .6H 2 O (0.290 g, 0.1 mmol) in 5 cm 3 of CH 3 CN was added dropwise to a hot stirred solution of the ligand L (0.030 g, 0.1 mmol) in a mixture of CH 3 OH/CH 3 CN (v/v = 2:1) and the mixture was stirred for 30 min. Diethyl ether was slowly diffused into the solution and block brown crystals suitable for X-ray diffraction analysis were collected by filtration within two weeks. and 0.96 (CH 3 ) Å and with U iso (H)= 1.2(1.5 for methyl)U eq (C). The water H atom was located on a difference Fourier map and refined isotropically.    The crystal packing of the title complex, viewed along the c axis. Hydrogen bonds are shown as dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq