Crystal structure of 210,220-bis(2,6-dichlorophenyl)-4,7,12,15-tetraoxa-2(5,15)-nickel(II)porpyhrina-1,3(1,2)-dibenzena-cycloheptadecaphane-9-yne dichloromethane monosolvate

In the crystal structure of the title compound, the NiII cations in the two unique complexes are coordinated in a square-planar coordination environment by the N atoms of a porphyrin molecule.


Chemical context
The crystal structures of several strapped (Peters et al., 2019), capped (Ganesh & Sanders, 1980), hindered (Momenteau et al., 1983) and bridged porphyrins (Battersby & Hamilton, 1980) have been determined. Strapped porphyrins are of extraordinary importance because they exhibit different structural features, which allow a wide range of applications (Goncalves & Sanders, 2007) and have been used as chiral epoxidation catalysts (Collman et al., 1995), as models for enzymes such as cytochrome P450 (Andrioletti et al., 1999), as building blocks for the synthesis of catenanes (Gunter et al., 1994), as building blocks for self-assembled photonic wires (Koepf et al., 2005), or as models for a number of biomimetic porphyrins (Morgan & Dolphin, 1987).

Structural commentary
The crystal structure of the title compound consists of discrete Ni-porphyrin complexes, in which the Ni II cations show a square-planar coordination (Fig. 2). The asymmetric unit consists of two complexes in general positions that show a significantly different conformation in their bridging side chain (Fig. 3). The Ni-N bond lengths are similar in both complexes and range from 1.937 (2) to 1.950 (3) Å (Table 1), in accordance with literature values (Liu et al., 2016). In both complexes, the Ni II cations are situated in the porphyrin ring plane (Fig. 3), with root-mean-square deviations of 0.0276 Å for molecule 1 (Ni1) and of 0.0186 Å for molecule 2 (Ni2). The 2,6-dichlorophenyl groups are nearly perpendicular to the corresponding porphyrin planes with dihedral angles of 89.82 (4) and 88.23 (4) (molecule 1) and 88.89 (5) and 85.82 (4) (molecule 2). This conformation is consolidated by intramolecular C-HÁ Á ÁCl hydrogen bonding between the methylene groups of the side chains and the Cl atoms of the 2,6-dichlorphenyl rings (Fig. 4, Table 2). In addition, the conformation of each side chain is stabilized by intramolecular C-HÁ Á ÁO bonding ( Table 2).
The asymmetric unit additionally contains two dichloromethane molecules in general positions, one of which is disordered (Fig. 2 Reaction scheme for the synthesis of the title compound.

Figure 5
Crystal structure of the title compound in a view along the a axis. The solvent molecules are omitted for clarity.

Figure 3
Side view of the two crystallographically independent complexes, showing the conformational differences in the side chains.

Figure 4
Crystal structure of the title compound showing intra-and intermolecular C-HÁ Á ÁCl hydrogen bonding as dashed lines. The disorder of one of the two crystallographically independent solvent molecules is not shown for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3.
The crystal metrics points to orthorhombic symmetry with the internal R-value only slightly higher in the orthorhombic system compared to the monoclinic system. Additionally, the ADDSYM option in PLATON (Spek, 2009) indicates a higher (pseudo)-symmetry for the monoclinic solution with 85% fit and missing n and c-glide planes, with Pccn as the most probable space group. Structure solution in Pccn led to two crystallographically independent molecules in the asymmetric unit that are each located on a twofold rotation axis. However, the acetylene side chain of one of these molecules is completely disordered around this axis, which indicates that   the crystal symmetry is too high. Moreover, structure refinement in Pccn led to very poor reliability factors with wR 2 values of about 50%, revealing that the true symmetry is in fact monoclinic. Therefore the structure was refined in the monoclinic space group P2 1 /c under consideration of twinning by pseudo-merohedry (mirror plane parallel to ab as twin element), which resulted in two crystallographically independent and fully ordered molecules, much better reliability factors and a BASF parameter of 0.5895 (8).

Computing details
Data collection: X-AREA (Stoe, 2008); cell refinement: X-AREA (Stoe, 2008); data reduction: X-AREA (Stoe, 2008); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010).  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell ESDS are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.