Syntheses, crystal structures and Hirshfeld surface analyses of (3aR,4S,7R,7aS)-2-(perfluoropyridin-4-yl)-3a,4,7,7a-tetrahydro-4,7-methanoisoindole-1,3-dione and (3aR,4S,7R,7aS)-2-[(perfluoropyridin-4-yl)oxy]-3a,4,7,7a-tetrahydro-4,7-methanoisoindole-1,3-dione

In each of the title compounds, the packing is driven by C—H⋯F intertactions, along with a variety of C—H⋯O, C—O⋯π, and C—F⋯π contacts. Hirshfeld surface analyses were conducted to aid in the visualization of these various influences on the packing.

The syntheses and crystal structures of the title compounds, C 14 H 8 F 4 N 2 O 2 and C 14 H 8 F 4 N 2 O 3 , are reported. In each crystal, the packing is driven by C-HÁ Á ÁF intertactions, along with a variety of C-HÁ Á ÁO, C-OÁ Á Á, and C-FÁ Á Á contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing: they showed that the largest contributions to the surface contacts arise from HÁ Á ÁF/FÁ Á ÁH interactions, followed by HÁ Á ÁH and OÁ Á ÁH/HÁ Á ÁO.

Chemical context
Polynorbornenes (PNBs), derived from ring-opening metathesis polymerization reactions, are numerous, owing to their relative ease of synthesis, tolerance of diverse functional groups and high-molecular weights with good processability (Isono et al., 2018). The use of dicarboxyimide-substituted norbornenes allows synthetic control of the substituents on the norbornene ring system, and this feature has been exploited for polymer light-emitting diodes (Zeng et al., 2018) and gas-separation membranes (Yu et al., 2016). With its predictable substitution chemistry (Baker & Muir, 2010;Chambers et al., 1988), perfluoropyridine was added to two dicarboxyimide-norbornene systems, and the resulting crystal structures are herein reported.

Structural commentary
Compound I crystallizes in the triclinic space group P1 with two molecules, A and B, per asymmetric unit, and compound II in the monoclinic space group P2 1 /n with one molecule per ISSN 2056-9890 asymmetric unit (Fig. 1). The synthesis of both compounds is conducted using endo starting materials, and the same configuration is observed in the resulting crystal structures. In I, steric interactions between the ortho-fluorine atoms and the carbonyl oxygen atoms prevents free rotation about the nitrogen-ipso-carbon bond (C3-N2 and C17-N4 in the crystal): this is evidenced by separate 19 F NMR peaks in solution for the ortho-F atoms (F2/F7 and F3/F6 in the crystal). In molecule A, the N1/C1-C5 plane is rotated by 58.05 (5) relative to the N2/C6/C7/C12/C13 plane and the corresponding dihedral angle for molecule B is 61.65 (7) . The addition of an oxygen atom between N2 and C3 in II alleviates this steric restriction and only one 19 F NMR peak in solution is observed for the ortho-F atoms; even so, the dihedral angle between the N1/C1-C5 and N2/C6/C7/C12/C13 planes in the crystal of II of 84.01 (5) is larger than those found in I.
Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was used to investigate the presence of hydrogen bonds and other intermolecular interactions in the crystal structures. The analyses and associated two-dimensional fingerprint plots ( Fig. 3) (Spackman & McKinnon, 2002) were generated with CrystalExplorer17.5 (Turner et al., 2017) using a standard surface resolution with the three-dimensional d norm surfaces plotted over a fixed color scale of À0.02500 (red) to 1.3800 (blue) a.u. The pale-red spots symbolize short contacts and negative d norm values on the corresponding surface plots shown in Fig. 2, associated with their relative contributions to the Hirshfeld surface.

Figure 1
The molecular structures of (a) I and (

Database survey
A search of the November 2018 release of the Cambridge Structure Database (Groom et al., 2016), with updates through May 2019, was performed using the program ConQuest (Bruno et al., 2002). The search was limited to organic structures with R 0.1. A search for tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione-based compounds with an aromatic substituent on the nitrogen atom yielded 58 results. The dihedral angle between the aromatic ring plane and the succinimide plane is bimodally distributed between 43 and 90 , with peaks near 60 and 75 . Hirshfeld surfaces of (a) I and (b) II mapped with d norm .

Figure 3
The overall two-dimensional fingerprint plots for (a) I and (b) II.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. H atoms were positioned geometrically and refined using a riding model with C-H = 0.95-1.0Å and U iso (H) = 1.2U eq (C).   For both structures, data collection: APEX3 (Bruker, 2017); cell refinement: SAINT (Bruker, 2017); data reduction:

Funding information
SAINT (Bruker, 2017); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.77 e Å −3 Δρ min = −0.41 e Å −3 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.