Crystal structure and Hirshfeld surface analysis of 2,4,6,11-tetrakis(4-fluorophenyl)-9-oxa-1,5-diazatricyclo[5.3.1.03.8]undecane

The compound, prepared by the NaBH4 reduction of 4,8,9,10-tetrakis(4-fluorophenyl)-1,3-diazaadamantan-6-one in chloroform and ethanol as solvent, crystallizes in the monoclinic space group P21/n with four molecules in the unit cell.


Chemical context
Molecules containing a bispidine nucleus are of great interest due to their presence in a wide variety of naturally occurring alkaloids and various biologically active molecules (Jeyaraman & Avila, 1981). The biological activities of the molecule depend crucially on the stereochemistry and conformation of the compound, and hence studies on the stereochemistry of the molecules are interesting. The title compound contains four fluorophenyl groups and hence the investigation also looked for any weak interactions involving fluorine which are of current interest (Hathwar et al., 2014). Moreover, Das et al. (2017) have recently discussed the role of halogens in stabilizing stacking patterns. ISSN 2056-9890

Supramolecular features
In the crystal, several C-HÁ Á ÁF hydrogen bonds occur. Screwrelated molecules are linked by C32-H32Á Á ÁF4 iii and C1-H1Á Á ÁF4 iii hydrogen bonds with F4 acting as a bifurcated acceptor (Table 1). The molecules are further linked by C31-H31Á Á ÁF1 i and C8-H8Á Á ÁF3 ii hydrogen bonds (Fig. 2). An N-HÁ Á Á interaction is present along with intra-and intermolecular C-HÁ Á Á interactions ( A view of the supramolecular architecture of the title compound. Some of the atoms have been omitted for clarity.

Figure 1
An ORTEP view of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at 40% probability level.

Hirshfeld surface analysis
Hirshfeld surface analysis and fingerprint plots, here generated with Crystal Explorer (Hirshfeld, 1977;Wolff et al., 2012;Turner et al., 2017), show the various intermolecular interactions present in crystal structures (Wiedemann & Kohl, 2017;Tarahhomi et al., 2013). Fig. 4 shows the Hirshfeld surface of the title compound mapped over d norm where the intense red spots indicate regions of donor-acceptor interactions (Cá rdenas- Valenzuela et al., 2018;Atiog lu et al., 2018) and represent the fluorine, carbon and hydrogen atoms involved. Fig. 5 shows the two-dimensional fingerprint plots, which quantify the contribution of each kind of interaction to the surface formation (McKinnon et al., 2007). The largest contribution to the surface of 37.9% is from HÁ Á ÁH contacts, while CÁ Á ÁH contacts contribute 22.4%; these represent van der Waals interactions present in the crystal. Intermolecular hydrogen-bonding interactions (FÁ Á ÁH/HÁ Á ÁF contacts) contribute 29.2%.  Table 1 Hydrogen-bond geometry (Å , ).

Database survey
Cg5 and Cg6 are the centroids of the C1-C6 and C10-C15 rings, respectively.

Figure 3
A view of the C11-H11Á Á Á interaction (intramolecular). Some of the atoms have been omitted for clarity.

Figure 4
Hirshfeld surface of the title compound plotted over d norm , with neighbouring interactions shown as red dashed lines.

Figure 5
Two-dimensional fingerprint plots for the title compound.

Synthesis and crystallization
The title compound was synthesized in three steps starting from 4-fluorobenzaldehyde, acetone and ammonium acetate. 4,8,9,10-Tetrakis(4-fluorophenyl)-1,3-diazaadamantan-6-one (1 mmol) dissolved in chloroform and NaBH 4 (1 mmol) dissolved in ethanol were mixed, transferred to a closed container and stirred at 278-283 K. The reaction was monitored by TLC, and after complete disappearance of the ketone the resulting mixture was filtered. The solvent was evaporated and washed with cold water to obtain the resulting product. The crude product was recrystallized from a chloroformethanol (1:2 v:v) mixture by the solvent diffusion method.