Bis{1-[3-(diethylammonio)propyliminomethyl]naphthalen-2-olato}nickel(II) dinitrate

The asymmetric unit of the title compound, [Ni(C18H24N2O)2](NO3)2, consists of one half of the centrosymmetric nickel(II) complex cation and a nitrate anion. The NiII atom, lying on an inversion center, is four-coordinated by the phenolate O atoms and imine N atoms of two Schiff base ligands, forming a square-planar geometry. The O- and N-donor atoms are mutually trans. In the crystal structure, the nitrate anions are linked to the complex cations by intermolecular N—H⋯O hydrogen bonds.

The compound consists of a centrosymmetric mononuclear nickel complex cation and two nitrate anions (Fig. 1). The Ni atom, lying on the inversion center, is four-coordinated by two phenolate O atoms and two imine N atoms from two Schiff base ligands, forming a square planar geometry. The bond lengths (Table 1) around the Ni atom are comparable to those observed in similar nickel complexes (Bhatia et al., 1983;Kamenar et al., 1990;Connor et al., 2003;Lacroix et al., 2004).
Experimental 2-Hydroxy-1-naphthaldehyde (0.1 mmol, 17.2 mg) and N,N-diethylpropane-1,3-diamine (0.1 mmol, 13.0 mg) were mixed and stirred in methanol (10 ml) for 30 min. Then a methanol solution (5 ml) of nickel nitrate (0.1 mmol, 29.1 mg) was added to the mixture. The final mixture was stirred for another 30 min to give a red solution. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of the solution at room temperature.

Refinement
H2 atom was located from a difference Fourier map and refined isotropically, with the N-H distance restrained to 0.90 (1) Å, and with U iso (H) fixed at 0.08 Å 2 . The remaining H atoms were positioned geometrically (C-H = 0.93-0.97 Å) and refined using a riding model, with with U iso (H) = 1.2U eq (C) and 1.5U eq (C metyl ). Rotating group models were used for the methyl groups.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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