Bis[2-(hydroxyiminomethyl)phenolato]nickel(II): a second monoclinic polymorph

The title compound, [Ni(C7H6NO2)2], (I), is a second monoclinic polymorph of the compound, (II), reported by Srivastava et al. [Acta Cryst. (1967), 22, 922] and Mereiter [Private communication (2002) CCDC refcode NISALO01]. The bond lengths and angles are similar in both structures. The molecule in both structures lies on a crystallographic inversion center and both have an internal hydrogen bond. The title compound crystallizes in the space group P21/c (Z = 2), whereas compound (II) is in the space group P21/n (Z = 2) with a similar cell volume but different cell parameters. In both polymorphs, molecules are arranged in the layers but in contrast to the previously published compound (II) where the dihedral angle between the layers is 86.3°, in the title polymorph the same dihedral angle is 29.4°. The structure of (I) is stabilized by strong intramolecular O—H⋯O hydrogen bonding between the O—H group and the phenolate O atom.

The title compound, [Ni(C 7 H 6 NO 2 ) 2 ], (I), is a second monoclinic polymorph of the compound, (II), reported by Srivastava et al. [Acta Cryst. (1967), 22, 922] and Mereiter [Private communication (2002) CCDC refcode NISALO01]. The bond lengths and angles are similar in both structures. The molecule in both structures lies on a crystallographic inversion center and both have an internal hydrogen bond. The title compound crystallizes in the space group P2 1 /c (Z = 2), whereas compound (II) is in the space group P2 1 /n (Z = 2) with a similar cell volume but different cell parameters. In both polymorphs, molecules are arranged in the layers but in contrast to the previously published compound (II) where the dihedral angle between the layers is 86.3 , in the title polymorph the same dihedral angle is 29.4 . The structure of (I) is stabilized by strong intramolecular O-HÁ Á ÁO hydrogen bonding between the O-H group and the phenolate O atom.
The cell dimensions of the title modification after transformation from P2 1 /c to P2 1 /n setting, are: a=18.062, b=7.472, c=4.991, β =105.39, whereas the cell dimensions of the reported compound (II) monoclinic P2 1 /n modification are: a = 13. 830, b = 4.880, c = 10.200 Å; β = 110.43° ( Srivastava et al., 1967). The asymmetric unit of the title compound contains half molecule ( Fig. 1), lying across a crystallographic inversion centre. The bond lengths and angles are within normal ranges (Allen et al., 1987) and are comparable with the structure of the compound (II).

Experimental
The title compound was prepared by direct synthesis: manganese powder (0.06 g, 1 mmol), Ni(OAc) 2 (0.25 g, 1 mmol), salicylic aldehyde (0.21 ml, 2 mmol), NH 2 OH . HCl (0.14 g, 2 mmol), dimethylformamide (20 ml) were heated to 323-333 K and stirred magnetically for 40 min, until total dissolution of the manganese powder was observed. The transparent brown solution was allowed to stand at room temperature and brown-green crystals of the title compound suitable for X-ray analysis precipitated within few days. They were collected by filter-suction, washed with dry Pr i OH and finally dried in vacuo at room temperature (yield; 0.12 g)

Refinement
The hydrogen atoms were located in difference Fourier synthesis and refined in isotropic aproximation.

Special details
Experimental. Numerical absorption corrections based on indexed crystal faces were applied using the Crystal Faces plugin in Bruker APEX2 software (Bruker, 2007) 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 mat-  (13)