Crystal structure of bis(2-{[(pyridin-2-yl)methylidene]amino}benzoato-κ3 N,N′,O)cobalt(II) N,N-dimethylformamide sesquisolvate

The coordination geometry around the central CoII ion is unexpectedly different from that for the co-crystal of the title molecule with anthranilic acid.


Chemical context
Metal complexes containing Schiff bases are the most fundamental chelating systems in coordination chemistry. Their interesting chemical and physical properties and their wideranging applications in numerous scientific areas have been explored widely (Vigato et al., 2012). During the last few years, we have investigated the chemistry of 3d metal complexes of Schiff base ligands with the aim of preparing mono-and heterometallic polynuclear compounds.
(M = Co, Ni, Zn) and anthranilic acid (Buvaylo et al., 2014b). The respective compounds were prepared by in situ Schiff base synthesis. ML 2 molecules of the isotypic CoL 2 ÁAAÁH 2 O and NiL 2 ÁAAÁH 2 O co-crystals retained the intramolecular distances M-(N,O) as found in the structure of the 'native' Schiff base metal complex NiL 2 ÁH 2 O (Mukhopadhyay & Pal, 2005). The crystal packing of the co-crystals was described as an insertion of the organic molecules between the layers of ML 2 complexes as they occur in the reported NiL 2 ÁH 2 O structure.
The title compound, [Co(C 13 H 9 N 2 O 2 ) 2 ]Á1.5C 3 H 7 NO, was prepared similarly to the co-crystals (Buvaylo et al., 2014b) but using additional [Cd(CH 3 COO) 2 ]Á2H 2 O in an attempt to prepare a heterometallic compound with HL. The obtained crystals, however, did not appear to contain anthranilic acid molecules or cadmium.

Structural commentary
The asymmetric unit of the title compound consists of one neutral CoL 2 molecule and 1.5 dimethylformamide (DMF) solvent molecules, of which one is fully ordered, the other being disordered about a crystallographic inversion centre. The CoL 2 molecule has no crystallographically imposed symmetry. The ligand molecules are deprotonated at the carboxylato oxygen atom and coordinate to the Co II atom through the azomethine, pyridine-N and carboxylato-O atoms in such a way that the metal atom is octahedrally surrounded by two anionic ligands with cis O atoms ( Fig. 1, Table 1). The octahedral geometry is severely distorted: the Co-(N,O) distances fall in the range 2.0072 (12)-2.1498 (14) Å , the trans angles at the Co II ion lie in the range 161.53 (6)-177.35 (5), the cis angles vary from 77.91 (5) to 103.70 (5) . Surprisingly, the coordination geometry around the Co II ion is markedly different from that of CoL 2 ÁAAÁH 2 O (Buvaylo et al., 2014b) where the Co-(N,O) distances range from 1.990 (2) to 2.088 (18) Å , and the trans and cis angles at the Co II ion vary from 167.96 (6) to 176.95 (7) and from 80.93 (7) to 98.81 (7) , respectively. The reason for such a discrepancy could be the absence of classical hydrogen bonds in the title compound in The molecular structure of the title complex, showing the atomnumbering scheme. Non-H atoms are shown as displacement ellipsoids at the 50% probability level.  Symmetry codes: (i) Àx þ 1; Ày þ 2; Àz þ 1; (ii) Àx þ 1; Ày þ 1; Àz þ 1; (iii) x; y À 1; z; (iv) Àx þ 1; Ày þ 2; Àz þ 2; (v) x; y þ 1; z.

Figure 2
Packing diagram showing alternating layers of [CoL 2 ] and DMF molecules. CH hydrogens have been omitted for clarity.
contrast to the co-crystal CoL 2 ÁAAÁH 2 O. A metal site with mixed (Co/Cd) occupancy for the title compound was ruled out by the refinement.

Supramolecular features
The crystal lattice is built of alternating layers of complex CoL 2 molecules and DMF molecules parallel to (010) (Fig. 2). Neighbouring CoL 2 molecules within a layer are related by an inversion centre with CoÁ Á ÁCo separations of 6.8713 (6) and 6.9985 (6) Å . Weak C-HÁ Á ÁO hydrogen-bonding interactions between the complex molecules and the solvent molecules lead to a consolidation of the crystal packing.

Synthesis and crystallization
The Schiff base ligand HL was prepared by refluxing pyridine-2-carbaldehyde (0.38 ml, 4 mmol) with anthranilic acid (0.55 g, 4 mmol) in 20 ml methanol for half an hour. The resultant yellow solution was left in open air overnight and used without further purification. To a stirred DMF solution (5 ml) of Cd(CH 3 COO) 2 Á2H 2 O (0.53 g, 2 mmol) in a 50 ml conic flask, HL (0.21 g, 4 mmol) in methanol from the previous preparation was added. The solution was magnetically stirred at 323 K for 20 minutes and a yellow precipitate of a Cd complex formed. Co(CH 3 COO) 2 Á-4H 2 O (0.25 g, 1 mmol) in DMF (10 ml) was added to the reaction mixture after a week. The mixture was stirred magnetically at 323 K for an hour, however, the yellow precipitate did not dissolve and was filtered off. The resulting red-brown solution was left to evaporate at room temperature. Red-brown block-like crystals of the title compound formed the next day. They were collected by filter-suction, washed with dry isopropanol and finally dried in vacuo (yield: 23% based on cobalt salt). Analysis for C 26 H 18 CoN 4 O 4 Á-1.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The refinement of the metal occupancy as part Co and part Cd gave 100% Co. One solvent DMF molecule was modelled as being disordered about a crystallographic inversion centre with resulting half-occupancy and with geometries restrained to ideal values. All hydrogen atoms were placed at calculated positions and refined by use of the riding-model approximation, with U iso (H) = 1.2U eq of the parent C atom.    (Agilent, 2011); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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. One solvent dmf molecule was modelled as being disordered about a crystallographic inversion centre. The geometries were restrained to ideal values.