Synthesis, structure and Hirshfeld surface analysis of 2-oxo-2H-chromen-6-yl 4-tert-butylbenzoate: work carried out as part of the AFRAMED project

In the title coumarin derivative, the dihedral angle between the 2H-chromen-2-one ring system and the phenyl ring is 89.12 (5)°. In the crystal, the molecules are linked by C—H⋯O hydrogen bonds into [010] double chains.


AFRAMED and chemical context
The AFRAMED (Supporting research and training in Africa through remote measurements; Abdel-Aal et al., 2023) CNRS project was developed by the Chair of the IUCr Africa Initiative (Professor Claude Lecomte) and his team for Crystallography Education in Africa.The project is based on the remote control by an African laboratory of a diffractometer based in France (in fact now at CRM2) to perform X-ray single-crystal diffraction measurements for research and teaching purposes.Selected crystals are sent to the French partner by African researchers who control the data collection remotely and then receive the intensity data by e-mail.The project was launched in August 2022 and is co-financed by the French Centre National de la Recherche Scientifique (CNRS), the United Nations Educational, Scientific and Cultural Organization (UNESCO), and the International Union of Crystallography (IUCr).Two main steps define AFRAMED: first, four weeks training of African Partners (young lecturers with permanent positions) on a single-crystal diffractometer, and in the second step, the African researchers' laboratories are focal points to assist their colleagues for remote measurements.To date, representatives of Algeria, Cameroon; Congo Brazzaville; Cote d'Ivoire, Egypt, Gabon and Senegal have been trained at the CRM2 laboratory of the Universite de Lorraine, France.This paper presents one of the results of this training: the synthesis, crystal structure and Hirshfeld surface analysis of the title coumarin derivative, I, synthesized by colleagues from Burkina Faso.Such coumaruin derivatives have various biological activities such as anticancer (Lacy et al., 2004;Kostova, 2005), anti-inflammatory (Todeschini et al., 1998), antiviral (Borges et al., 2005), anti-malarial (Agarwal et al., 2005), anti-glaucoma (Ziki et al., 2023) and anticoagulant (Maurer et al., 1998) properties.

Structural commentary
As shown in Fig. 1, the C1-C9/O1/O2 2H-chromen-2-one ring system of I is almost planar (r.m.s.deviation = 0.044 A ˚) and the dihedral angle between this ring system and the C11-C16 phenyl group in the 4-tert-butylbenzoate moiety is 89.12 (5) � .This near perpendicular orientation has been observed in other coumarin derivatives with the same motif (Ji et al., 2016).The dihedral angles between the linking C10/C11/O3/O4 ester group and the pendant C1-C9/O1/O2 and C11-C16 groupings are 64.38 (5) and 25.05 (6) � , respectively, indicating that the major twist in the molecule occurs about the C8-O3 bond.An inspection of the bond lengths shows that there is a slight asymmetry of electronic distribution around the coumarin ring: the difference between the C2 C3 [1.343 (2) A ˚] and C1-C2 [1.449 (2) A ˚] separations confirms the double-bond character of the former as indicated in the chemical scheme.Atom C20 of the tert-butyl group lies close to the plane of its attached ring [deviation = 0.226 (2) A ˚] whereas C18 and C19 are displaced either side of the ring [deviations = À 1.465 (1) and 0.964 (1) A ˚, respectively].

Supramolecular features
In the crystal, the molecules of I are connected by C-H� � �O hydrogen bonds (Table 1) to build double chains propagating in the [010] direction: this motif results in two adjacent R 2 2 (8) loops between each pair of molecules in one chain formed by the C3, C6 and C9 hydrogen bonds (Fig. 2).The C16 hydrogen bond provides the linkage to the second chain (Fig. 3).The The molecular structure of I with displacement ellipsoids drawn at the 50% probability level.Murthy et al., 1988) and 4-methyl-2-oxo-2H-chromen-6-yl benzoate (YEFSOU; Ji et al., 2017).ATORUZ only features a C6-H6� � �O3 hydrogen bond because a methyl group is bonded to C9 (according to the numbering scheme of I).This prevents the formation of layers like those found in the packing of I, although similar layers are found in GASXON.

Hirshfeld surface and Fingerprint plots
The interactions mentioned above are confirmed by the twodimensional fingerprint plots of I (Fig. 5).The greatest contributions are the H� � �H and H� � �O/O� � �H contacts with 46.7 and 24.2%, respectively.The H� � �C/C� � �H and C� � �C contacts contribute 16.7 and 7.6%, respectively.The contri-butions of the H� � �H interactions in I to Hirshfeld surface are greater than those found in 2-oxo-2H-chromen-3-yl 4chlorobenzoate (Ziki et al. 2017); this can be related to the packing of the 2H-1-chromen-6-yl moieties of I.The H� � �O/ O� � �H contacts are related to the C-H� � �O1 hydrogen bonds shown in Fig. 2. Their contact points are shown in red and are labelled on the Hirshfeld surface (see Fig. 5a).

Synthesis and crystallization
To 30 ml solution of 4-tert-butylbenzoyl chloride (1.2 g; 6.17 mmol) in dry tetrahydrofuran, were added dry triethylamine (2.6 ml; 3.1 mmol) and 6-hydroxycoumarin (1.00 g; 6.17 mmol) in small portions over 30 min.The mixture was then refluxed for 4 h and poured into 40 ml of chloroform.The solution was acidified with diluted hydrochloric acid until the pH was 2.5.The organic layer was extracted, washed with water to neutrality, dried over MgSO 4 and the solvent removed.The resulting precipitate was suction filtered, washed with petroleum ether and recrystallized from chloroform solution to give colorless prismatic crystals of I in a yield of 84%.

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. Fractional Figure 1

Figure 2
Figure 2 Fragment of a [010] chain in the structure of I showing the hydrogen bonds involving C3, C6 and C9 as black dashed lines.

Figure 3
Figure 3 Partial packing diagram for I showing [010] double chains arising from C-H� � �O hydrogen bonds (black dashed lines in one chain, magenta dashed lines in the other and the C16 cross-linking bonds in blue).

Figure 4
Figure 4The unit-cell packing for I viewed down [010].

Figure 5 (
Figure 5 (a) Hirshfeld surface of I mapped over d norm and (b) two-dimensional fingerprint plots of (b) overall and delineated into contributions from different contacts: (c) H-H, (d) H-O/O-H, (e) H-C/C-H and (f) C-C.

Table 2
Experimental details.
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