A second monoclinic polymorph of {2,6-bis[(2,4,5-trifluorophenyl)iminomethyl]pyridine-κ3 N,N′,N′′}dichloridonickel(II)

The asymmetric unit of the title compound, [NiCl2(C19H9F6N3)], contains one half-molecule residing on a crystallographic twofold rotation axis. The title compound crystallizes in space group C2/c while the previously reported polymorph was reported in P21/c [Baldovino-Pantaleón et al. (2006 ▶). Adv. Synth. Catal. 348, 236–242]. The Ni2+ ion exhibits a pentacoordinate distorted trigonal–bipyramidal NiCl2N3 geometry, with two Cl atoms in the equatorial plane. In the crystal, molecules are linked by intermolecular C—F⋯π [F⋯centroid = 2.9676 (14) Å] interactions.


Experimental
Crystal data [NiCl 2 (C 19 H 9  A second monoclinic polymorph of {2,6-bis [(2,4,5-trifluorophenyl) The selection of these ligands has been done on the basis of the robustness that they confer to the transition metal complexes they form (Baldovino-Pantaleón, et al., 2005, 2006. In recent years this kind of complexes have gained more interest particularly those derived from Ni, due to the importance that cross-coupling reactions have gained in important organic transformations of potential industrial relevance and the potential application of the nickel derivatives for the same sort of process regularly catalized by analogous palladium derivatives, but using a far more cheaper metal (Gómez-Benítez et al., 2006). The title compound is a polymorphous of a compound described previously (Baldovino-Pantaleón, et al., 2006).
The molecular structure of I is shown in figure 1 with the numbering scheme. In comparison, compound II described previously (Baldovino-Pantaleón, et al., 2006), was crystallized in a monoclinic (P 2 1 /c), while compound I, crystallizes in space group C 2/c. The asymmetric unit consists of a half molecule with Ni-N1-C4-H4 in a special position (1/2, y, 1/4), and by two fold axis the complete molecule is generated. The Ni atom is found in a pentacoordinated distorted bipyramidal geometry with the two chlorides occupying the equatorial positions. While the fragment N1-Ni-N2-N2A is planar, the pyridine ring is slightly rotated by 5.4 (1)°. The 2,4,5-trifluorophenyl ring is not coplanar and is forming a dihedral angle of 39.41 (5)° with the coordination metallic center, while in II, the fluorophenyl rings have dihedral angles of 14.4 (2)°a nd 13.4 (2)° with the coordination metallic center. The bond distances Ni-N(imino) in I are slightly shorter than in II.
In absence of clasic aceptor-donor H atom, the weak interactions become very important stabilizing the crystal structure.
The molecules in the crystal structure are linked by C-H-F-C, C-H-π, C-F-π and C-F-F-C intermolecular interactions (Table 1).

Experimental
A solution of the ligand {C 5 H 3 N-2,6-(CH=N-C 6 H 2 -2,4,5-F 3 ) 2 } (120 mg, 0.33 mmol) in anhydrous CH 2 Cl 2 (10 ml) was added to a stirred solution of NiCl 2 .6 H 2 O(0.078 g, 0.33 mmol) in absolute methanol (10 ml). The resulting green solution was stirred at room temperature for 2 h. After this time a red suspension is noted and the solvent evaporated under vacuum.
The product was purified by recrystallization from MeOH; the resulting precipitated was filtered and washed with hexane (3 X 5 ml) and dried under vacuum. Crystals suitable for single-crystal X-ray diffraction studies were obtained from a dichloromethane/ methanol (4:1) solution. A red solid was obtained; yield: 142 mg (88%); mp: 240°C