Crystal structure of 5,15-bis(4-methylphenyl)-10,20-bis(4-nitrophenyl)porphyrin nitrobenzene disolvate

The whole molecule of the title porphyrin, which crystallized as a nitrobenzene disolvate, is generated by inversion symmetry. In the crystal, the porphyrin molecules are linked by C—H⋯O hydrogen bonds, forming chains along [100]. The solvent molecules are also linked by C—H⋯O hydrogen bonds, forming chains along [100]. Interdigitation of the p-tolyl groups along the c axis creates rectangular channels in which the solvent molecules are located.


Chemical context
Porphyrins and their metallated derivatives have been studied extensively for their host-guest properties (Byrn et al., 1991), catalytic activity (Shultz et al., 2009) and for applications in dye-sensitized solar cells (Urbani et al., 2014). The presence or absence of a metal ion at the porphyrin core can greatly affect its physical properties, such as catalytic activity and crystal packing. The title compound is the free-base analogue of a previously reported zinc derivative (Adilov & Thalladi, 2007). The absence of the metal ion alters the crystal packing and these changes in the crystal structure of its nitrobenzene disolvate are discussed herein. ISSN 2056-9890

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The asymmetric unit consists of half of the porphyrin molecule and one nitrobenzene solvent molecule. The whole molecule of the porphyrin is generated by inversion symmetry. The porphyrin macrocycle is almost planar, the maximum deviation from the mean plane of the non-hydrogen atoms being 0.0970 (19) Å for atom C1 (and the symmetry-related atom). The dihedral angles between the porphyrin ring mean plane and the aryl rings at the meso positions are similar; 74.84 (6) for the nitrophenyl rings and 73.37 (7) for the tolyl rings.

Supramolecular features
In the crystal, the solvent molecules are linked by C-HÁ Á ÁO hydrogen bonds [2.58 (5) Å , 129.9 (3) ] forming chains along the a-axis direction ( Fig. 2 and Table 1). The nitrophenyl groups of the macrocyle are projected into the interlayer space where an oxygen of a nitro group (O2) forms a C-HÁ Á ÁO hydrogen bond [2.453 (3) Å , 158.6 (2) ] with neighbouring molecules, leading to the formation of chains along [100] ( Fig. 2 and Table 1). Interdigitation of the p-tolyl groups along the c-axis creates rectangular channels in which the solvent molecules are located, as illustrated in Fig. 3.

Figure 1
The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Unlabelled atoms are related to labelled atoms by inversion symmetry (symmetry operation: Àx, 2 À y, Àz), and only one solvent molecule is shown.
est. While CEZTUX has the same 1:2 porphyrin-solvent ratio, it has a totally different crystal packing. Both structures, however, contain porphyrin layers and the solvent molecules are intercalated between the layers. In the title free-base, the nitro groups of the macrocycle form C-HÁ Á ÁO hydrogen bonds with neighbouring molecules resulting in continuous offset stacks along the a-axis direction. The same situation is observed in the crystal of the tetrakis(4-nitrophenyl) analogue, BOMTEE.

Synthesis and crystallization
The synthesis of the title compound has been described previously (Adilov & Thalladi, 2007). It crystallized as a nitrobenzene disolvate on slow evaporation of a solution in chloroform/nitrobenzene (v:v 1:2).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound and N-bound H atoms were included in calculated positions and refined as riding atoms: C-H = 0.95-0.98 Å , N-H = 0.88 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (N, C) for other H atoms. The two NH H atoms in the porphyrin core are disordered over the four pyrrole N-atoms, and were refined with occupancies of 0.5 each. A view along the a axis of the interlayer stacking in the crystal of the title compound, also showing the intercalation of the nitrobenzene groups between the layers. Data collection: SMART (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SIR2004 (Burla et al., 2007); program(s) used to refine structure: Olex2.refine (Bourhis et al., 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009), SHELXTL (Sheldrick, 2008) and publCIF (Westrip, 2010).  0.0240 (9) 0.0308 (