{6,6′-Diethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenolato}nickel(II) monohydrate

In the title complex, [Ni(C23H28N2O4)]·H2O, the NiII ion is coordinated by the N2O2 unit of the tetradentate Schiff base ligand in a slightly distorted planar geometry. The asymmetric unit of the title compound comprises one complex molecule and a water molecule of crystallization. The H atoms of the water molecule make bifurcated intermolecular hydrogen bonds with the O atoms of the phenolate and ethoxy groups with R 1 2(5) and R 1 2(6) ring motifs, which may, in part, influence the molecular configuration. The dihedral angle between the two benzene rings is 31.43 (5)°. The crystal structure is further stabilized by intermolecular C—H⋯O and C—H⋯π interactions, which link neighbouring molecules into one-dimensional extended chains along the a axis. An interesting feature of the crystal structure is the short intermolecular C⋯C [3.3044 (14) Å] contact which is shorter than the sum of the van der Waals radii.

In the title complex, [Ni(C 23 H 28 N 2 O 4 )]ÁH 2 O, the Ni II ion is coordinated by the N 2 O 2 unit of the tetradentate Schiff base ligand in a slightly distorted planar geometry. The asymmetric unit of the title compound comprises one complex molecule and a water molecule of crystallization. The H atoms of the water molecule make bifurcated intermolecular hydrogen bonds with the O atoms of the phenolate and ethoxy groups with R 1 2 (5) and R 1 2 (6) ring motifs, which may, in part, influence the molecular configuration. The dihedral angle between the two benzene rings is 31.43 (5) . The crystal structure is further stabilized by intermolecular C-HÁ Á ÁO and C-HÁ Á Á interactions, which link neighbouring molecules into one-dimensional extended chains along the a axis. An interesting feature of the crystal structure is the short intermolecular CÁ Á ÁC [3.3044 (14) Å ] contact which is shorter than the sum of the van der Waals radii.

Comment
Schiff base complexes are some of the most important stereochemical models in transition metal coordination chemistry, with their ease of preparation and structural variations (Granovski et al., 1993). Metal derivatives of Schiff bases have been studied extensively, and copper(II) and Ni(II) complexes play a major role in both synthetic and structural research (Elmali et al., 2000;Blower, 1998;Granovski et al., 1993;Li & Chang, 1991;Shahrokhian et al., 2000). Tetradentate Schiff base metal complexes may form trans or cis planar or tetrahedral structures (Elmali et al., 2000).
The Ni II ion of the title compound ( Fig. 1), shows a sligthly distorted planar geometry which is coordinated by two imine N atoms and two phenol O atoms of the tetradentate Schiff base ligand. The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable with the related structures (Clark et al., 1968(Clark et al., , 1969(Clark et al., , 1970. The asymmetric unit of the title compound comprises one molecule of complex and a water molecule of crystallization. The hydrogen atoms of the water molecule make bifurcated intermolecular hydrogen bonds with the oxygen atoms of the phenolato-and ethoxy groups with R 2 1 (5) and R 2 1 (6) ring motifs (Bernstein et al., 1995), which may, in part, influence the molecular configuration. The dihedral angle between the two benzene rings is 31.43 (5)°. The crystal structure is further stabilized by intermolecular C-H···O and C-H···π interactions which link neighbouring molecules into 1-D extended chains along the a axis. The interesting feature of the crystal structure is a short intermolecular C7···C17 i [3.3044 (14) Å] contact which is shorter than the sum of the van der Waals radius of a carbon atom. The crystal structure is further stabilized by intermolecular C-H···O and C-H···π interactions ( Table 2, Cg1 and Cg2 are the centroids of the C12-C17 and C1-C6 benzene rings) which link neighbouring molecules into 1-D extended chains along the b-axis (Fig. 2).

Refinement
The water H-atoms were located from the difference Fourier map and freely refined. The rest of the hydrogen atoms were positioned geometrically [C-H = 0.95-99 Å] and refined using a riding approximation model with U iso (H) = 1.2 or 1.5U eq (C).
A rotating-group model was used for the methyl groups of the ethoxy substituents.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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  (  supplementary materials sup-9