Fluorenonophane chlorobenzene solvate: molecular and crystal structures

The molecular and crystal structures of the chlorobenzene solvate of fluorenonophane have been studied using X-ray diffraction analysis. The fluorenonophane contains two fluorenone fragments linked by two m-substituted benzene fragments. Some decrease in its macrocyclic cavity leads to a stacking interaction between the tricyclic fluorenone fragments. In the crystal, the fluorenonophane and chlorobenzene molecules are linked by weak C—H⋯π(ring) interactions and C—H⋯Cl hydrogen bonds.


Chemical context
Discovered at the end of the last century, the ability of cyclophanes to form inclusion complexes makes them the central class of synthetic receptors in molecular recognition processes (Diederich, 1991). Particular attention has been paid to the possibility of cationic cyclophanes with box geometries being involved in strong donor-acceptor interactions leading to the formation of 'guest-host' complexes with different guests (Dale et al., 2016;Barnes et al., 2013;Gong et al., 2010). Previously we have obtained fluorenonophane 1 with two fluorenone fragments linked by rigid xylyl groups (Lukyanenko et al., 2003;Simonov et al., 2006). X-ray diffraction analysis of this cyclophane revealed the box geometry with an open intramolecular cavity and the formation of inclusion complexes with DMF and nitrobenzene (Simonov et al., 2006). The other fluorenonophane obtained by our group, 2, differs from the previous one in the position of the methylene groups, which are located directly at the benzene fragment in 1 or fluorenone in 2. Fluorenonophane 2 forms inclusion complexes with chloroform and bromoform with a 1:2 stoichiometry. Moreover, C-ClÁ Á Á and C-BrÁ Á Á halogen bonds (Shishkina et al., 2021) are present in the complexes. In contrast to cationic cyclophanes, there are no charged fragments in fluorenonophanes. Continuing our research in this area, we have obtained fluorenonophane 3 with a different position of attachment of the benzene rings compared to 2 (m-and p-isomers, respectively) and studied its complexation with chlorobenzene. ISSN 2056-9890

Supramolecular features
In the crystal, the fluorenonophane and chlorobenzene molecules are linked to each other by weak C46-H46Á Á ÁO6 and C18-H18Á Á ÁCl1 hydrogen bonds while the fluorenophanes are linked by weak C35-H35Á Á ÁO1 hydrogen bonds (Table 1), forming stepped ribbons. The ribbons are connected by C1-H1AÁ Á ÁCg2 and C22-H22AÁ Á ÁCg1 interactions (Table 1) to give the final three-dimensional structure. The halogen atom does not form a halogen bond in the structure of 3, in contrast to the supramolecular complexes studied earlier (Shishkina et al., 2021). The electrostatic potential for chlorobenzene was calculated using the B3LYP/6-311 G(d,p) method. An area with a positive charge (-hole) was not found in the electrostatic potential map around the halogen atom (Fig. 2). The highest electrostatic potential at the chlorine atom is À0.08 eV. This fact can explain the absence of halogen bonds in the structure of 3.

Figure 2
Electrostatic potential map of the chlorobenzene molecule in 3 calculated by the B3LYP/6-311 G(d,p) method.

Figure 1
The molecular structure of the title compound showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 50% probability level. and a fixed colour scale of À0.134 (red) to 1.206 (blue) were generated separately ( Fig. 3) for the fluorenonophane and chlorobenzene molecules. The areas in red correspond to contacts that are shorter than the sum of the van der Waals radii of the closest atoms. Thus, the red spots at some hydrogen atoms and at the carbonyl oxygen atom as well as in the area of the five-membered ring indicate the existence of short C-HÁ Á ÁO and C-HÁ Á Á(ring) contacts.
To evaluate the contribution of the short contacts of different types to the total Hirshfeld surface, two-dimensional fingerprint plots for the fluorenonophane and chlorobenzene molecules were generated (Fig. 4). The contribution from the CÁ Á ÁH/HÁ Á ÁC contacts corresponding to the C-HÁ Á Á(ring) interactions are represented by a pair of sharp spikes (27.7% and 25.9% for fluorenonophane and chlorobenzene, respectively). Analysis of the fingerprint plots also showed a significant contribution from OÁ Á ÁH/HÁ Á ÁO contacts (19.7%) associated with the C-HÁ Á ÁO hydrogen bonds.

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.42, update of November 2020; Groom et al., 2016) for cyclophanes containing fluorenone and benzene fragments yielded two hits: two structures with fluorenone fragments linked by rigid xylyl groups (CCDC 263272 and CCDC 263273;Simonov et al., 2006). Recently, two more structures with fluorenonophanes linked by para-substituted benzene fragments were published (CCDC 647971 and CCDC 2098245; Shishkina et al., 2021). The structures found are characterized by a larger macrocyclic cavity compared to that in fluorenonophane 3.

Synthesis and crystallization
A solution of 1.75 g (4.78 mmol) of 2,7-bis(bromomethyl)-9Hfluoren-9-one (Haenel et al., 1985) in 200 mL of anhydrous DMF was added to a mixture of 0.526 g (4.78 mmol) of resorcinol and 3.96 g (28.7 mmol) of K 2 CO 3 in 270 mL of anhydrous DMF with stirring under nitrogen for 10 h at 353-358 K. The reaction mixture was stirred at the same temperature for a further 35 h, cooled and filtered (Fig. 5) The two-dimensional fingerprint plots for fluorenonophane 3 (top) and chlorobenzene (bottom).

Figure 3
Hirshfeld surface mapped over d norm showing the conformation of the fluorenonophane and chlorobenzene molecules.

Refinement
Crystal data, data collection, and structure refinement details are summarized in Table 2. Carbon-bound H atoms were added in calculated positions with C-H bond lengths of 0.95 Å for C-H, 0.92 Å for CH 2 and refined as riding atoms with U iso (H) = 1.2U eq (C). The synthesis of fluorenonophane 3    (9) 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.