Crystal structures of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin as the chloroform monosolvate and tetrahydrofuran monosolvate

The crystal structures of the title compounds, two solvates (CHCl3 and THF) of a symmetric and highly substituted porphyrin, OBrTPFPP, are described. These structures each feature a non-planar porphyrin ring, exhibiting a similar conformation of the strained ring independent of solvent identity. These distorted porphyrins are able to form hydrogen bonds and sub-van der Waals halogen interactions with enclathrated solvent; supramolecular interactions of proximal macrocycles are additionally affected by solvent choice.


Chemical context
Highly substituted porphyrins are a subclass of porphyrin compounds where the meso and positions are substituted with non-H atoms. When large substituents are introduced to the periphery of the porphyrin ring, this tends to overcrowd the macrocycle and induce conformational distortion, increasing with the steric demand (Senge & Kalisch, 1997;Medforth et al., 1992). Among the most studied substitution patterns are those with variously functionalized aryl rings at the 5,10,15,20-positions and with halogen, alkane and aryl substituents at the 2, 3,7,8,12,13,17,18-positions (Senge, 2000(Senge, , 2006 There are numerous approaches used to introduce conformational distortion to porphyrins, including coordination of specific metal centers, incorporation of a strapping motif, or decorating the ring with sterically demanding substituents (Schindler et al., 2018;Senge, 2006). Recent publications show uses for distorted porphyrins as free-base catalysts and sensors, and these compounds demonstrate unique and tuneable porphyrin inner core interactions (Aoki et al., 2019;Norvaiša et al., 2019;Kielmann et al., 2019;Kielmann & Senge, 2019). For example, non-planar metal-free porphyrins show promise as organocatalysts, acting as hydrogen-bond donors (Kielmann et al., 2019). Moreover, the porphyrin scaffold is customizable, and the potential for tuneable basicity and catalytic activity based on variable substitution patterns has been explored (Roucan et al., 2017). The distortion of the porphyrin ring, when compared to the planar parent compound, affects the photophysical and electronic properties of both free-base macrocycles and of derived metal complexes (Parusel et al., 2000;Gentemann et al., 1994;Rö der et al., 2010). With this in mind, halogenated porphyrins specifically are of interest as ligands in catalytic metal complexes, owing to non-planar conformation, as well as the electron-deficient character of the porphyrin ring (Dolphin et al., 1997;Henling et al., 1993).
The title compound has been previously characterized as a dichlorobenzene solvate (Takeuchi et al., 1994). Structural differences between this literature compound and the structures presented herein arise from intermolecular interactions with chloroform and THF. Additionally, in the published structure, the solvent could not be adequately modelled. These three structures are compared below.

Structural commentary
The crystal structure of the title compound (2,3,7,8,12,13,-17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin monochloroform solvate, (1ÁCHCl 3 ) shows a single H 2 OBrTPFPP molecule and one chloroform solvate in the asymmetric unit. This highly substituted porphyrin ring exhibits peri interactions from the appended bromine atoms crowding with pentafluorophenyl rings, forcing the bromine atoms substantially out of the mean plane of the porphyrin ring at a mean deviation of 2.14 (14) Å . One of these pentafluorophenyl rings is disordered over two positions, related by a co-planar shift; the co-crystallized CHCl 3 is also disordered over two orientations. A view of the molecular structure of H 2 OBrTPFPP is shown in Fig. 1.
A second crystal structure of (2, 3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin monotetrahydrofuran solvate (1ÁTHF) displays essentially the same conformation of the macrocycle; differences in the packing of these compounds are discussed below. The Á24 values, a summation of atomic deviations from mean plane of the macrocycle are similar in 1ÁCHCl 3 and 1ÁTHF; a view of the skeletal deviations from the mean-plane in the crystal structure of these two compounds is shown in Fig. 4b.
Normal Structure Decomposition (NSD, Jentzen et al., 1995;Schindler et al., 2018) analysis is the standard method of comparing the mode and extent of distortion between porphyrin structures. NSD is the decomposition of the atomic coordinates of a porphyrin into defined in-plane and out-ofplane distortion modes, based on a least-squares fit of the atomic coordinates to the calculated lowest frequency vibrational modes. The porphyrin rings of the title compounds are shown to exhibit significant out-of-plane saddle-type [B 2u (min)] distortion in both crystal structures reported here. This saddling distortion is a direct result of large substituents appended to the porphyrin ring -the saddle distortion alleviates steric demand by removing the restraint of coplanarity from the Br and aryl groups. Slight isotropic contraction, or bre mode distortion, of this porphyrin ring when projected into the xy-plane [A 1g (min)] is an effect of the large skewing, or pyrrole tilt -the reported Cl 8 TPFPP and F 8 TPFPP porphyrins do not show this A 1g contraction with similar bond distances reported, as shown in Table 3
This solvent-mediated supramolecular motif serves to arrange the porphyrin rings directly above and below one another, in an approximately face-to-face arrangement. As a result of this arrangement, the porphyrin molecules form stacks which extend along the b-axis direction. The adjacent stacks of porphyrin units in the ac direction interdigitate with one another, as shown in Fig. 3.
In 1ÁTHF, the central core of the porphyrin displays traditional hydrogen bonding (Table 2) from one pyrrole group to the THF oxygen atom [NÁ Á ÁO 2.849 (6) Å ], with a longer distance to the other available pyrrole N-H group (NÁ Á ÁO = 3.8 Å ). The THF solvate is not observed to form similar bimodal intramolecular interactions as the chloroform solvate, and porphyrin molecules do not form the infinite stacking arrangements seen in 1ÁCHCl 3 . The porphyrin molecules display multiple halogen-halogen interactions from the bromine and fluorine atoms in both structures.
The macrocycle structures of 1ÁCHCl 3 and 1ÁTHF can be directly compared to the previous structure 1ÁC 6 H 4 Cl 2 ; these three structures all exhibit approximately the same macrocycle bond distances and angles, shown in Table 3. The supramolecular interactions of 1ÁC 6 H 4 Cl 2 could not be reliably determined given that the solvent was only partially modelled in the reported structure. The face-to-face stacking centroidto-centroid distance of porphyrin macrocycles in 1ÁC 6 H 4 Cl 2 was 6.93 Å , whereas for 1ÁCHCl 3 , the separation was 6.83 Å . It is additionally possible that the solvent in the former case was in fact dichloromethane, which was present in the crystallization solution and displays a similar ClÁ Á ÁCl separation.
The NSD analysis parameters of similar literature structures are summarized in Fig. 5, as a comparator to the structures in this work. The NSD parameter, in Å , is equal to one quarter of the sum of the displacements of all 24 atoms of the simplified distortion model, which can be attributed to this distortion mode; the error value shown is the sum error (oop) of the least-squares fit of all six lowest frequency modes. As expected, an increasing saddle-type distortion is found for increasing size of the halogen atom, with little deviation from planarity apparent where X = H or F [sad = À0.001 (9) Å (H) and 0.000 (0) Å (F)]. Significant saddling distortion was apparent for X = Cl [sad = 1.91 (2) Å ], and greater for X = Br [1ÁC 6 H 4 Cl 2 sad = 2.72 (5) Å , 1ÁCHCl 3 sad = 3.45 (7) Å and 1ÁTHF sad = 3.16 (7)], showing the dependence of distortion on steric bulk, which outweighs solvent contributions.

Synthesis and crystallization
This compound was synthesized by a previously reported procedure (Mandon et al., 1992). Crystallization was performed by slow evaporation of a partially covered homogeneous solution at room temperature; of chloroform for 1ÁCHCl 3 and THF for 1ÁTHF.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4.
Compound 1ÁCHCl 3 was refined as an inversion twin, with a Flack parameter of 0.010 (4), indicating a small inversion impurity in the single crystal. The pentafluorophenyl group bound to C5 was modelled as disordered over two equivalent [0.462 (7):0.538 (7)] coplanar positions, displaced by '0.3 Å at the centroid, which were constrained to have equal U ij parameters for atoms sharing sites, similar U ij parameters for bonded atoms, and idealized ring geometry. The most distant fluorine atoms had to be held to additional isotropic U ij restraints. The chloroform solvate was also modelled as disordered over two orientations, sharing approximate carbon and hydrogen positions. This second orientation was related by a partial rotation around the threefold axis and modelled such that these two orientations had a sum occupancy of one molecule. The dominant orientation was refined to 0.882 (7) occupancy, and C-Cl distances in the minor component had to be restrained to idealized bond distances. C atoms were held to equal U ij restraints and Cl atoms were restrained to similar U ij parameters.
In compound 1ÁTHF pentafluorophenyl rings were modelled as disordered over two orientations with dominant orientations of 0.748 (18) and 0.694 (17) occupancy. Porphyrin-to-phenyl distances and carbon atom displacement parameters (U ij ) were restrained. Idealized geometric constraints were imposed on the least occupied phenyl ring C10A-C10F. The ipso phenyl carbon atoms were constrained  Table 3 Calculated mean distances, angles and structural parameters (Å , ) for compounds 1-6.
Measured mean bond distances, angles, mean-plane angles, calculated NSD values, intramolecular contacts and mean-plane deviations for atom groups. to have equal U ij parameters and positions. Pyrrole hydrogen atoms were located in the difference-Fourier map and restrained using idealized bond distances.

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.