(2,3,7,8,12,13,17,18-Octaethylporphyrinato-κ4 N)cobalt(II)–2-nitrobenzaldehyde (1/2)

The asymmetric unit of the title compound, [Co(C36H44N4)]·2C7H5NO3, is composed of one half of the complex, arranged about an inversion center, and a complete 2-nitrobenzaldehyde (NBA) molecule. The structure consists of columns that contain interleaved molecules of NBA and [CoII(OEP)] (OEP is 2,3,7,8,12,13,17,18-octaethylporphyrin), which are stacked along the a axis. The CoII atom is involved in a π interaction with the ring of the NBA molecule with a centroid–metal distance of 3.508 (6) Å. There is an intramolecular C—H⋯O hydrogen bond in the NBA molecule.

The asymmetric unit of the title compound, [Co(C 36 H 44 N 4 )]Á-2C 7 H 5 NO 3 , is composed of one half of the complex, arranged about an inversion center, and a complete 2-nitrobenzaldehyde (NBA) molecule. The structure consists of columns that contain interleaved molecules of NBA and [Co II (OEP)] (OEP is 2, 3,7,8,12,13,17,18-octaethylporphyrin), which are stacked along the a axis. The Co II atom is involved in a interaction with the ring of the NBA molecule with a centroid-metal distance of 3.508 (6) Å . There is an intramolecular C-HÁ Á ÁO hydrogen bond in the NBA molecule.
It is known that OEP metalloporphyrins can be dimerized as is the case of the [Fe III (OEP)(NO)] + complex (Ellison et al., 2000). For this species the distance between two adjacent porphyrinato mean plans is 3.41 Å which indicated a strong π-π interaction. This complex forms a tight cofacial π-π dimer in the solid state.The most interesting feature of (I), is the rather strong π-interaction between the cobalt metal of the [Co II (OEP)] and the centroid of the phenyl rings of the nitrobenzaldehyde molecule (Figure 1) where the Co···Cg intermolecular distance is 3.508 Å (Cg is the centroid of the phenyl ring of the NBA molecule) and the angle between this distance and the perpendicular from the cobalt to the plane of the phenyl is 23.39 ° ( Table 2). The cobalt atom is nearly perpendicular to the C101 atom ( Figure 2). This structure present a striking resemblance with the one of the [Co II (F 28 TPP)].2tol complex (Olmstead et al., 2003) where the cobalt atom is centered roughly at the midpoint at the two adjacent carbons bonds in the toluene rings and the Co-C distances are 3.05 and 3.13 Å. It is noteworthy that the structure of (I) consists of columns that contain interleaved molecules of NBA and [Co II (OEP)] which are stacked a long the crystallographic a axis (Figure 3).

Experimental
[Co II (OEP)] (Scheidt & Tyrk, 1994) (100 mg, 0.17 mmol) and nitrobenzaldehyde (190 mg, 1.26 mmol) in 25 ml of chlorobenzene were stirred over night at room temperature. The color changes from red-pink to dark red and crystals of complex (I) were prepared by slow diffusion of hexanes into the chlorobenzene solution.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl), 0.97 Å (methylene) or 0.93 Å (aromatic) with U iso (H) = 1.2U eq (C aromatic, methylene ) or U iso (H) = 1.5U eq (C methyl ). The coordinates of the H atom attached to the aldehyde function have been refined freely with U iso (H) = 1.2U eq (C).

Figure 1
Perspective drawings from the X-ray crystal structure determination of (I) that highlights π-interraction between the [Co II (OEP)] complex and the 2-nitrobenzaldehyde molecule. H atoms have been omitted for clarity.    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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq