Crystal structure of bis{2-[(E)-(4-methoxylbenzyl)iminomethyl]phenolato-κ2 N,O 1}nickel(II)

The NiII atom in the title compound shows a square-planar NiN2O2 coordination with the imine N and phenolate O atoms of the two Schiff base ligands. C—H⋯O and C—H⋯π interactions result in the formation of sheets of molecules parallel to the ac plane.


Chemical context
Schiff bases have often been used as chelating ligands in coordination chemistry as they readily form stable complexes with most transition metal ions (Kalita et al., 2014;Mohamed et al., 2010). Metal complexes of Schiff bases containing nitrogen and other donor atoms have received attention because of their stability, biological activity (Islam et al., 2014) and potential applications in other fields, such as catalysis (Mohd Tajuddin et al., 2012).

Structural commentary
The asymmetric unit of (I) consists of an Ni II cation that lies on an inversion centre and a Schiff base anion that functions as a bidentate ligand (Fig. 1). The N 2 O 2 donor set of the chelating Schiff base ligands has the N1 and O1 donor atoms mutually trans, in a distorted square-planar coordination geometry, with O1-Ni1-N1 = 92.30 (4) and O1-Ni1-N1 i = 87.70 (4) [symmetry code: (i) Àx + 1, Ày, Àz + 1] and a maximum deviation from the NiN 2 O 2 least-squares plane of 0.731 (1) Å for the N1 atom. The Ni1-N1 and Ni1-O1 bond lengths in the N 2 O 2 coordination plane are 1.9191 (11) and 1.8407 (9) Å , respectively. These are similar to those observed in the other closely related Ni II complexes with N 2 O 2 -coordinating Schiff base ligands (Bahron et al., 2011;Mohd Tajuddin et al., 2010). Other bond lengths and angles observed in the structure are also normal. The methoxy substituent is coplanar with the ring to which it is bound, the C15-O2-C12-C13 torsion angle being 3.93 (2) . The plane of the methoxybenzene ring (C9-C14) makes a dihedral angle of 84.92 (6) with that of the phenolate benzene ring (C1-C6). A weak intramolecular C14-H14Á Á ÁO1 contact is also observed that affects the overall molecular conformation.

Supramolecular features
In the crystal (Fig. 2), molecules are linked into screw chains by weak C11-H11AÁ Á ÁO2 interactions ( Fig. 2 and Table 1). Additional C5-H5AÁÁÁCg1 contacts link molecules into chains along the c-axis direction ( Fig. 3 and Table 1) resulting in sheets parallel to the ac plane and stacked along the b axis (Fig. 4).

Database survey
A search of the Cambridge Structural Database (Version 5.35, November 2013 with 3 updates; Allen, 2002) reveals a total of 1191 Ni II complexes with an NiN 2 O 2 coordination sphere. No fewer than 333 of these had the Ni II atom chelated by two 3-(iminomethyl)phenolate residues. No corresponding structures with a benzyl or substituted benzyl unit bound to the imino N atom were found. However, extending the search to allow additional substitution on the phenolate ring resulted Screw chains of molecules of (I) linked by C-HÁ Á ÁO contacts (shown as dashed lines). Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
C-HÁ Á Á contacts for (I), shown as dotted lines, with ring centroids shown as coloured spheres. Cg1 is the centroid of the C1-C6 ring.

Figure 1
The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme. The symmetry-related Schiff base ligand is generated by the symmetry code (Àx + 1, Ày, Àz + 1).

Bis{2-[(E)-(4-methoxylbenzyl)iminomethyl]phenolato-κ 2 N,O 1 }nickel(II)
Crystal data 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.