Crystal structure of (15,20-bis(2,3,4,5,6-pentafluorophenyl)-5,10-{(4-methylpyridine-3,5-diyl)bis[(sulfanediylmethylene)[1,1′-biphenyl]-4′,2-diyl]}porphyrinato)nickel(II) dichloromethane x-solvate (x > 1/2)

The title compound consists of discrete complexes with a square-pyramidal NiN5 coordination polyhedron for the metal ions. The complexes are linked by C—H⋯F hydrogen bonds into chains propagating along [001].

The title compound, [Ni(C 64 H 33 F 10 N 5 S 2 )]ÁxCH 2 Cl 2 , consists of discrete Ni II porphyrin complexes, in which the five-coordinate Ni II cations are in a distorted square-pyramidal coordination geometry. The four porphyrin nitrogen atoms are located in the basal plane of the pyramid, whereas the pyridine N atom is in the apical position. The porphyrin plane is strongly distorted and the Ni II cation is located above this plane by 0.241 (3) Å and shifted in the direction of the coordinating pyridine nitrogen atom. The pyridine ring is not perpendicular to the N 4 plane of the porphyrin moiety, as observed for related compounds. In the crystal, the complexes are linked via weak C-HÁ Á ÁF hydrogen bonds into zigzag chains propagating in the [001] direction. Within this arrangement cavities are formed, in which highly disordered dichloromethane solvate molecules are located. No reasonable structural model could be found to describe this disorder and therefore the contribution of the solvent to the electron density was removed using the SQUEEZE option in PLATON [Spek (2015). Acta Cryst. C71, 9-18].

Chemical context
Ni II porphyrins are emerging in a number of applications including photoswitchable MRI contrast agents (Venkataramani et al., 2011;Dommaschk et al., 2014Dommaschk et al., , 2015a, redox catalysts (Eom et al., 1997;Han et al., 2015) or catalysts in the hydrogen evolution reaction (HER) (Han et al., 2016;Solis et al., 2016;Maher et al., 2019). The axial coordination of Ni II porphyrins has been studied extensively regarding the underlying equlibria (Caughey et al., 1962;McLees & Caughey, 1968;Walker et al. 1975), conformational changes (Jia et al., 1998) and photo-induced complex formation and dissociation . Moreover, the axial coordination determines the spin state of these complexes (Renner et al., 1991;Jentzen et al., 1995). Upon coordination of one axial ligand, Ni II porphyrins undergo spin transition from a diamagnetic (S = 0) square-planar, low-spin (LS) state with a coordination number (CN) of four (CN4) to a paramagnetic (S = 1), square-pyramidal (CN5), high-spin (HS) state. The CN5 HS complex is further stabilized by the coordination of a sixth ligand, resulting in minor changes of the spectroscopic properties of the CN6 complexes compared to their CN5 counterparts. The coordination and de-coordin- ISSN 2056-9890 ation of axial ligands are observed in a fast dynamic equilibrium, dominated by the CN4 and the CN6 species (Kadish et al., 2000 andKruglik et al., 2003). The spectra and properties of a well defined five-coordinate (CN5) Ni II porphyrin in solution and the solid state was described recently (Gutzeit et al., 2019a). In closely related, tightly strapped Ni II porphyrins, the coordination of the axial pyridine ligand is dependent on the geometry of the ligand-containing strap (Kö bke et al., 2019). Furthermore, the coordination behaviour is dependent on the para substituent of the pyridine moiety due to its electronic influence (Dommaschk et al., 2014). Hence, a para methyl substituent was introduced in the complex described previously (Gutzeit et al., 2019a) to improve the intramolecular coordination. The modified synthesis yielded the title compound as a byproduct (Gutzeit et al., 2019a;Kö bke et al., 2019) similar to the synthesis of the unsubstituted derivative (Gutzeit et al., 2019b). Metallation was achieved under standard conditions. Splitting of the CH 2 -proton signals in the 1 H NMR spectrum are observed for the unmetallated porphyrin and the title compound due to an impeded ring inversion of the strap (Gutzeit et al., 2019b). The increased paramagnetic shifts of the -pyrrole H atoms ( min = 8.8 ppm, max = 49.0 ppm, CDCl 3 , 298 K; Gutzeit et al., 2019a) of the title compound (45.9 ppm) compared to the compound without a methyl group in para position of the pyridine ring (42.2 ppm) indicates an increase of intramolecular coordination by 9% ( Fig. 1; Gutzeit et al., 2019a), confirming the influence of the para methyl substituent.

Structural commentary
In the crystal structure of the title compound, (C 64 H 33 F 10 N 5 NiS 2 ) (CH 2 Cl 2 ) x , the five-coordinate Ni II cations are bound by the four nitrogen atoms of the porphyrin molecule and the nitrogen atom of the pyridine ring . The porphyrin plane is distorted due to steric constraints of the strap, similar to the unsubstituted derivative (Gutzeit et al., 2019b). The maximum deviation of the individual atoms from the mean plane calculated through the porphyrin atoms amounting to 0.137 (3) Å for the parent compound (Gutzeit et al., 2019b) is increased to 0.159 (4) Å in the title compound. The Ni-N bond lengths to the porphyrin nitrogen atoms [2.031 (3)-2.041 (3) Å ] are significantly shorter than that to the pyridine nitrogen atom (Table 1). In the title compound, the Ni II cation is shifted 0.241 (3) Å out of the porphyrin N4 plane towards the pyridine nitrogen atom, which is slightly shorter than that in the derivative without the methyl group [0.250 (3) Å , Fig. 5]. This is also the case for the Ni-N distance to the pyridine N atom of 2.106 (3) Å , compared to 2.112 (2) Å in the derivative. The angle between the planes of the pyridine ring and the N 4 porphyrin plane amounts to 67.1 (2) , which is very different from that in the derivative without the methyl group [80.48 (6) ; Fig. 5]. The tilt of the pyridine ring does not impede the intramolecular coordination, which is reflected by the short Ni-N py (py = pyridine) distance and the NMR shift. The tilt of the axial ligand is reinforced by packing effects leveraged by the para methyl group. This is also in agreement with a different conformation Comparison of the paramagnetic shifts of the -pyrrole H atoms of the parent compound and the title compound, indicating increased intramolecular coordination.

Figure 2
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. of the overall porphyrin molecule compared to the unsubstituted derivative, because the pentafluoro phenyl rings are more perpendicular to the porphyrin N4 plane with dihedral angles of 82.53 (8) and 77.37 (7) , which is also the case for the phenyl rings [67.0 (1) and 83.4 (2) ; Figs. 3 and 4]. Finally, the dihedral angles between the biphenyl rings are 72.3 (2) and 64.3 (2) compared to 63.2 (1) and 53.5 (1) in the derivative. Overall, the increased steric demand of the para methyl substituent increases the distortion compared to the unsubstituted derivative.

Supramolecular features
In the extended structure of the title compound, the complexes are linked by C-HÁ Á ÁF hydrogen bonds into zigzag chains that extend in the [001] direction with adjacent complexes related by a 2 1 -screw-axis (Fig. 6). The C-HÁ Á ÁF angle is 164 , indicating a relative strong interaction (Table 2). By this arrangement, cavities are formed, in which the disordered dichloromethane solvate molecules are located. There are additional intramolecular C-HÁ Á ÁN contacts, with angles far from linearity that correspond to only very weak interactions (Table 2).

Database survey
According to a search of the Cambridge Structural Database, only four crystal structures of five-coordinate Ni II porphyrins have been reported (Kumar & Sankar, 2014;Dommaschk et al., 2015c;Gutzeit et al., 2019a,b; refcodes DOJPAV01, QUZVAK, COCBAA and HOPSIR, respectively). The square-pyramidal complex geometry is predominant in zinc (Paul et al., 2003;Deutman et al., 2014) and iron (Awasabisah et al., 2015;Yu et al., 2015) porphyrins. Zinc porphyrins form five-coordinate complexes additionally with oxygencontaining ligands (Leben et al., 2018), a behaviour uncommon in Ni II porphyrins (Ozette et al., 1997). The conformation of the porphyrin (Flanagan et al., 2015;Senge, 2011) has been recognized as an important factor for the axial coordination, spin state (Thies et al., 2010;Dommaschk et al., 2014) and catalytic activity (Ramesh et al., 2016)  Molecular structure of the title compound showing the orientation of the pyridine ring relative to the N 4 plane.

Figure 3
Molecular structure of the title compound viewed onto the porphyrin plane.

Figure 4
Molecular structure of the title compound showing the square-pyramidal Ni II coordination. Table 2 Hydrogen-bond geometry (Å , ).

Synthesis and crystallization
The free base porphyrin of the title compound was obtained as a byproduct of a variant of the published procedure (Gutzeit et al., 2019a;Kö bke et al., 2019). The free base porphyrins were separated by column chromatography (silica gel, dichloromethane; silica gel, dichloromethane/n-pentane, 1:1 and silica gel, toluene) and precipitated from dichloromethane by diffusion of methanol (59 mg, 3%).  (43)  The nickel cation was introduced under standard conditions (31 mg porphyrin, 68 mg Ni(acac) 2 , 30 ml toluene, reflux, 21 h) followed by filtration through a pluck of silica (dichloromethane) and precipitation from dichloromethane by diffusion of methanol. The crystals were washed with methanol and n-pentane (11 mg, 34%).  Red blocks of the title compound were obtained by dissolving the complex in dichloromethane and gas-phase diffusion of methanol.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-H hydrogen atoms were located in difference maps but were positioned with idealized geometry (C-H = 0.95-0.98 Å ) and refined isotropically with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl) using a riding model.
After structure refinement using a model with one Ni porphyrin complex and a half dichloromethane solvate molecule disordered around a center of inversion, there was significant residual electron density that definitely corresponds to additional dichloromethane disordered over several orientations. A number of different split models were tried using restraints for the geometry and for the components of the anisotropic displacement parameters, but no reasonable structural model was found and very large anisotropic displacement parameters were obtained. Therefore, the contribution of this solvent to the electron density was removed with SQUEEZE in PLATON (Spek, 2009(Spek, , 2015, which leads to a reasonable structure model and very good reliability factors. By this procedure, the amount of dichloromethane cannot accurately be determined and there is indication that this position is not fully occupied, which is highly likely because this solvate is very unstable and already starts to decompose during the sample preparation.  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 (Sheldrick, 2008) and Diamond (Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010).  (7) 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.

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