Crystal structure of (15,20-bis(2,3,4,5,6-pentafluorophenyl)-5,10-{(pyridine-3,5-diyl)bis[(sulfanediylmethylene)[1,1′-biphenyl]-4′,2-diyl]}porphyrinato)nickel(II) dichloromethane x-solvate (x > 1/2) showing a rare CN5 coordination

The crystal structure of the title compound consists of discrete complexes with a five-coordinate Ni cation and intramolecular hydrogen-bonded dichloromethane solvent molecules that are linked into dimers via pairs of intermolecular C—H⋯S hydrogen bonds.

The crystal structure of the title compound, [Ni(C 63 H 31 F 10 N 5 S 2 )]ÁxCH 2 Cl 2 (x > 1/2), consists of Ni-porphyrin complexes that are located in general positions and dichloromethane solvent molecules that are disordered around centers of inversion. The Ni II ions are in a square-pyramidal (CN5) coordination, with four porphyrin N atoms in the equatorial and a pyridine N atom in the apical position and are shifted out of the porphyrine N 4 plane towards the coordinating pyridine N atom. The pyridine substituent is not exactly perpendicular to the N 4 plane with an angle of intersection between the planes planes of 80.48 (6) . The dichloromethane solvent molecules are hydrogen bonded to one of the four porphyrine N atoms. Two complexes are linked into dimers by two symmetry-equivalent C-HÁ Á ÁS hydrogen bonds. These dimers are closely packed, leading to cavities in which additional dichloromethane solvent molecules are embedded. These solvent molecules are disordered and because no reasonable split model was found, the data were corrected for disordered solvent using the PLATON SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18].

Chemical context
Nickelporphyrins and their axial coordination have been studied from a number of different viewpoints over the last six decades. Their rich coordination behaviour (Caughey et al., 1962;McLees & Caughey, 1968;Walker et al. 1975), conformations (Jia et al., 1998) and photophysics  has attracted interest in different fields, including as model compounds for the F430 cofactor (Renner et al., 1991) or heme (Jentzen et al., 1995), for applications in solar energy conversion (Shelby et al., 2014), in hydrogenevolution (Han et al., 2016) or redox catalysis (Eom et al., 1997) and as responsive MRI contrast agents (Venkataramani et al., 2011;Dommaschk et al., 2014aDommaschk et al., ,b, 2015a. Squareplanar [coordination number (CN) 4] nickelporphyrins are diamagnetic, (S = 0), low-spin (LS) complexes. Upon coordination of one (CN5) or two (CN6) axial ligands such as pyridine or piperidine, the nickel cation undergoes spin transition to the high-spin (HS) state. This coordination-induced spin-state switch (CISSS) leads to a drastic change in the spectra and properties of the HS complexes. The coordination and decoordination of the axial ligands in solution is a fast dynamic equilibrium (Kadish et al., 2000). Thus, the observed ISSN 2056-9890 properties are dependent on the speciation in the equilibrium defined by the association constants (K 1S , K 2 ; Thies et al., 2010). In these equilibria, the dominating species are the CN4 and CN6 complexes, with the CN5 species only formed by up to 10% of porphyrins in solution (Kruglik et al., 2003). Thus, the characterization of CN5 nickelporphyrins was restricted to transient UV-vis  and resonance Raman measurements (Findsen et al., 1986;Kim et al., 1986) so far. Recently, the first exclusively five-coordinate (CN5) nickel porphyrin in solution, including its structure in the crystal phase, were presented , offering a new approach towards afore-mentioned applications. The axial ligand of the CN5 porphyrin is held in the coordination position by a rigid strap, inducing conformation-dependent spin-state switching. Similar strapped nickelporphyrins showed incomplete axial coordination in solution (Kö bke et al., 2019). The title compound ( Fig. 1) was obtained as a byproduct in the synthesis of a CN5 porphyrin with a similar structure  and was metallated under standard conditions. Preorientation of the ligand by the ligand-holding strap should favour Ni coordination. However, 1 H NMR spectropscopy (500 MHz, CDCl 3 , 298 K) indicates incomplete intramolecular coordination (82% CN5 HS, 18% CN4 LS) of the title compound. One application is pH measurements in non-aqueous solutions because coordination and NMR signals are dependent on the protonation state of the pyridine moiety. The NMR spectra revealed an unexpected behaviour of the title compound, because the geminal coupling of the CH 2 -protons indicates confined movement of the pyridine moiety and hindered ring inversion of the strap (see Figure S1 in the supporting information).

Structural commentary
In the crystal structure of the title compound, [Ni(C 63 H 31 F 10 N 5 S 2 )]ÁxCH 2 Cl 2 (x > 1/2), the Ni II ions are coordinated by the four N atoms of the porphyrine moiety within a square-planar ligand field and the Ni coordination is completed by a pyridine N atom in the apical position, leading to a square-pyramidal coordination environment (CN5) (Figs. 1-3). The porphyrine ring plane is not fully planar with maximum deviations of the C atoms from the mean plane of 0.137 (3) Å . The Ni cation is shifted by 0.250 (3) Å out of the N 4 plane towards the coordinating pyridine N atom (Fig. 4). The Ni-N bond lengths (Table 1) to the porphyrine N atoms ranges from 2.0350 (17) to 2.0434 (17) Å and are in agreement with values retrieved from literature, indicating that the Ni II ion is in the high-spin state (Thies et al., 2010). The Ni-N bond length to the pyridine N atom of 2.1122 (17) Å is significantly longer and agrees well with the 2.11 Å that are observed in the CN5 porphyrin . Compared to octahedral (CN6) nickelporphyrins with two axial pyridine ligands, the Ni-N distance is shortened by $0.10 Å (Thies et al., 2010). The pyridine ring is not exactly perpendicular to the N4 plane (Fig. 4), the angle of intersection between them amounting to 80.48 (6) , in good agreement with similar complexes (Thies et al., 2010). The tetrafluorophenyl rings are rotated out of the N 4 plane by 67.43 (5) and 68.74 (6) , and the phenyl rings (C39-C44 and C58-C63) by 58.82 (6) and 72.59 (5) , respectively. The dihedral angles between the biphenyl units amount to 63.02 (9) and 53.45 (8) .

Supramolecular features
In the crystal structure of the title compound, the discrete Ni porphyrine complexes are linked into dimers via centrosym- Molecular structure of the title compound with the atom labelling and displacement ellipsoids drawn at the 50% probability level. The H atoms and the solvent molecules are omitted for clarity. metric pairs of intermolecular C-HÁ Á ÁS hydrogen bonds between the porphyrine H atoms and the sulfur atoms ( Fig. 5 and Table 2). Between the dimers, cavities are formed that are occupied by the dichloromethane solvent molecules, which are disordered about centers of inversion. These solvent molecules are linked by intermolecular C-HÁ Á ÁCl hydrogen bonding to the nitrogen atom N1 of the porphyrine unit that is not shielded by the strap (Fig. 5). The C-HÁ Á ÁS angle is close to linearity, indicating that this is a relatively strong interaction ( Crystal packing of the title compound with a view of a centrosymmetric dimer with intermolecular hydrogen bonding shown as dashed lines. The two orientations of the disordered dichloromethane molecule are shown with black and grey bonds. Table 2 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 1; Ày þ 1; Àz þ 1.

Figure 2
Molecular structure of the title compound in a view onto the porphyrin plane.

Figure 3
Molecular structure of the title compound with view of the Ni coordination.

Figure 4
Side view of the complex showing the orientation of the pyridine ring relative to the N 4 plane. The intermolecular hydrogen bond is shown as dashed line and the disorder of the dichloromethane molecule is omitted for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-H hydrogen atoms were located in difference-Fourier maps but were positioned with idealized geometry and refined with isotropic with U iso (H) = 1.2U eq (C) using a riding model. After structure refinement using a model with one Ni porphyrine complex and a half dichloromethane solvent molecule disordered about a center of inversion, there was significant residual electron density that definitely corresponded to an additional dichloromethane molecule that was 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 structure model was found and very large anisotropic displacement parameters were obtained. Therefore, the contribution of this solvent to the electron density was removed with the SQUEEZE (Spek, 2015) routine in PLATON, which leads to a reasonable structure model and very good reliability factors. Their formula mass and unit-cell characteristics were not taken into account during refinement. By this procedure, the amount of dichloromethane cannot be determined accurately and there is indication that this position is not fully occupied, which is highly likely because this solvent is very unstable and starts to decompose during the sample preparation.   SHELXL2014 (Sheldrick, 2015b); molecular graphics: XP (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.