Crystal structure of bis(bis{(E)-[(6-{(E)-[(4-fluorobenzyl)imino]methyl}pyridin-2-yl)methylidene](4-fluorophenyl)amine}nickel(II)) tetrabromide nonahydrate

In the title complex, [Ni(C21H17F2N3)2]2Br4·9H2O, there are two independent metal complexes per asymmetric unit and two ligands per metal complex. The structural features (bond lengths and angles) of the two complexes are almost identical. In each complex, the nickel(II) ion is coordinated in an octahedral environment by six N atoms from two chelating (9E)-N-({6-[(E)-(4-fluorobenzylimino)methyl]pyridin-2-yl}methylene)(4-fluorophenyl)methanammine ligands. The Ni—N bond lengths range from 1.973 (2) to 2.169 (2) Å, while the chelate N—Ni—N angles range from 77.01 (10) to 105.89 (9)°. Additionally, there are four bromide anions and nine solvent water molecules within the asymmetric unit. The water molecules form a hydrogen-bonded network, displaying C—H⋯O, C—H⋯Br, O—H⋯Br, O—H⋯O and O—H⋯F interactions into layers parallel to (111). In each unit, the fluorophenyl rings of one ligand are stacked with the central ring of the other ligand via π–π interactions, with the closest centroid-to-plane distances being 3.445 (5), 3.636 (5), 3.397 (5) and 3.396 (5) Å.


S1. Chemical context
Schiff bases are the condensation product of an amine and an active carbonyl compound which are capable of forming coordination complexes with transition metal ions (Vigato et al., 2004;Gupta et al., 2008). In particular, metal complexes derived from Schiff bases with multiple binding sites are effective in many biochemical and antimicrobial applications (Skyrianou et al., 2010).

S3. Supramolecular features
Intermolecular interactions form various C-H···O, C-H···Br, O-H···Br, O-H···O and O-H···F bonds (Table 1 and Figure 2). In each unit, there are also π-π interactions between the fluorophenyl rings of one ligand and the central ring of the other ligand.

S4. Synthesis and crystallization
2,6-diformylpyridine (0.500 g, 3.70 mmol) and 4-fluorobenzylamine (845.8 µL, 7.40 mmol) were separately dissolved in 10 mL methanol. The two solutions were slowly mixed in 20 mL methanol with constant stirring over 10 minutes at room temperature following the similar method as described earlier (Işıklan et al., 2011 The nickel complex was obtained by mixing of the ligand (0.349 g, dissolved in 5 mL of methanol) and nickel(II) bromide hydrate (0.1092 g, dissolved in 5 mL of water) in water-methanol (50 mL) over 10 minutes under constant stirring at room temperature. After reducing the solvent to about 10 mL, diethyl ether was added dropwise. The precipitate thus obtained was filtered and washed with diethyl ether, providing a brownish product (0.3902 g, 92.7 % yield). Single crystal suitable for X-ray analysis was grown from the slow evaporation of the complex (107 mg) dissolved in water-methanol (10 mL, v/v, 1:1) after three weeks.

S5. Refinement details
The H atoms bonded to carbons were placed in calculated positions and treated as riding, C-H = 0.95 to 0.99 Å, with U iso (H) = 1.2U eq (C). H atoms bonded to O were restrained to have similar O-H lengths and H-O-H angles.

Figure 1
Asymmetric unit of the title compound showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Crystal packing of the title compound viewed along the a axis showing hydrogen-bonding interactions as dashed lines.

Figure 3
Part of the crystal structure of compound (I) showing the π-π-stacking between fluorophenyl rings and the central pyridine ring.

Bis(bis{(E)-[(6-{(E)-[(4-fluorobenzyl)imino]methyl}pyridin-2-yl)methylidene](4-fluorophenyl)amine}nickel(II))
tetrabromide nonahydrate Hydrogen site location: difference Fourier map H atoms treated by a mixture of independent and constrained refinement 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.