domain: chim.cris chim phys

text:
Patrice Kenfack Tsobnang

Eric Ziki

Soso Siaka

Jules Yoda

Seham Kamal

Adam Bouraima

Djifa Ayi

Emmanuel Hounsi

El-Eulmi Wenger

Claude Bendeif

Lecomte

Hounsi

Emmanuel Wenger

El-Eulmi Bendeif

Claude Lecomte
email: claude.lecomte@univ-lorraine.fr

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

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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 singlecrystal diffraction measurements for research and teaching purposes. Selected crystals are previously 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 Inter-national 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 Université 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 anti-cancer (Lacy et al., 2004;Kostova, 2005), antiinflammatory (Todeschini et al., 1998), anti-viral effect (Borges et al., 2005), anti-malarial (Agarwal et al., 2005), anti-glaucoma (Ziki et al., 2023) and anti-coagulant (Maurer et al., 1998) properties.

Structural commentary

As shown in Figure 1, the C1-C9/O1/O2 2H-chromen-2-one ring system of I is almost planar (r.m.s. deviation = 0.044 Å) and the dihedral angle between this ring system and the C11-C16 phenyl group in the 4-tert-butyl-benzoate 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

Supra-molecular 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 R2 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 pendant 4-tert-butyl-benzoate moieties are parallel and

Database survey

A search of the Cambridge Structural Database (CSD) for structures having a coumarin motif similar to that of I returned five hits for to the following molecules:

4-methyl-2-oxo-2H-1-benzo-pyran-6-yl pyridine-2- carboxyl-ate (CSD refcode ATOROT), 4-methyl-2-oxo-2H-1-benzo-pyran-6-yl pyridine-3-carboxyl-ate (ATORUZ), 4-methyl-2-oxo-2H-1-benzo-pyran-6-yl pyridine-4-carboxyl-ate (ATOSAG), 6-
acet-oxy-coumarin (GASXON) and 4-methyl-2-oxo-2H-chromen-6-yl benzoate (YEFSOU). ATORUZ only features a C6-H•••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 inter-actions mentioned above are confirmed by the two-dimensional fingerprint plots of I ( Fig. 5).

The greatest contributions are the H inter-actions in I to Hirshfeld surface are greater than those found in 2-oxo-2H-chromen-3-yl 4chloro-benzoate (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

Synthesis and crystallization

To 30 ml solution of 4-tert-butyl-benzoyl chloride (1.2 g; 6.17 mmol) in dry tetra-hydro-furan, were added dry tri-ethyl-amine (2.6 ml; 3.1 mmol) and 6-hy-droxy-coumarin (1.00 g; 6.17 mmol) in small portions over 30 min. The mixture was then refluxed for four hours and poured into 40 ml of chloro-form. The solution was acidified with diluted hydro-chloric acid until the pH was 2.5. The organic layer was extracted, washed with water to neutrality, dried over MgSO4 and the solvent removed. The resulting precipitate was suction filtered, washed with petroleum ether and recrystallized from chloro-form solution to give colorless prismatic crystals of I in a yield of 84%.

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 1. The H atoms were located in difference maps and their positions and Uiso values were freely refined. Computer programs: APEX3 [START_REF] Bruker | APEX3, SADABS and SAINT[END_REF], SAINT [START_REF] Bruker | APEX3, SADABS and SAINT[END_REF], SHELXT (Sheldrick, 2018), SHELXL2018/3 (Sheldrick, 2018), ORTEP-3 [START_REF] Farrugia | [END_REF], publCIF (Westrip, 2010).

Table 2. Hydrogen-bond geometry (Å, º) for (I) D-H•••

A D-H H•••A D•••A D-H•••A C9-H9•••O1 i 0.

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 atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) for (I)

  (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) Å] and C1-C2 [1.441 (2) Å] 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) Å] whereas C18 and C19 are displaced either side of the ring [deviations = -1.465 (1) and 0.964 (1) Å, respectively].

Figure 1 .

 1 Figure 1. The molecular structure of I with displacement ellipsoids drawn at the 50% probability level.

  shifted by translation along the b axis. Aromatic p•••p stacking inter-actions between centrosymmetric pairs of C4-C9 rings reinforce the cohesion of the double chains [centroid-centroid separation = 3.6301 (8), slippage = 1.579 Å]. The unit-cell packing of I can be described as a tilted herringbone motif (Fig. 4), as also observed in the crystal structure of 1-(1,2-di-hydro-phthalazin-1-yl---idene)-2-[1-(thio-phen-2yl)ethyl---idene]hydrazine (Majoumo-Mbe et al. 2019).

Figure 2 .

 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 .

 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 .

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

  Fig. 2. Their contact points are shown in red and are labelled on the Hirshfeld surface (see Fig. 5a).

Figure 5 .

 5 Figure 5. (a) Hirshfeld surface of I mapped over dnorm 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 1 .

 1 Experimental details

	Crystal data
	Chemical formula	C20H18O4
	Mr	322.34
	Crystal system, space group	Monoclinic, C2/c
	Temperature (K)	100
	a, b, c (Å)	35.908 (4), 6.8473 (6), 13.2661 (11)
	b (°)	98.915 (4)
	V (Å 3 )	3222.3 (5)
	Z	8
	Radiation type	Mo Ka
	m (mm -1 )	0.09
	Crystal size (mm)	0.20 × 0.15 × 0.08
	Data collection
	Diffractometer	Bruker D8 Venture
	Absorption correction	Multi-scan
		(SADABS; Bruker, 2019)
	Tmin, Tmax	0.731, 0.895
	No. of measured, independent and	60054, 4940, 3518
	observed [I > 2s(I)] reflections
	Rint	0.061
	(sin q/l)max (Å -1 )	0.716
	Refinement
	R[F 2 > 2s(F 2 )], wR(F 2 ), S	0.044, 0.124, 1.11
	No. of reflections	4940
	No. of parameters	289
	H-atom treatment	All H-atom parameters refined
	Dρmax, Dρmin (e Å -3 )	0.30, -0.27

Acknowledgements

The authors thank PMD 2 XX-ray diffraction facility (https://crm2.univ-lorraine.fr/plateformes/pmd2x/) of the Institut Jean Barriol, Université de Lorraine, for X-ray diffraction measurements and the AFRAMED project. CCDC is also thanked for providing access to the Cambridge Structural Database through the FAIRE program.

supporting information

Synthesis, structure and Hirshfeld surface analysis of 2-oxo-2H-chromen-6-yl 4-tert-butyl-benzoate: work carried out as part of the AFRAMED project Patrice Kenfack Tsobnang, Eric Ziki, Soso Siaka, Jules Yoda, Seham Kamal, Adam Bouraima, Ayi Djifa Hounsi, Emmanuel Wenger, El-Eulmi Bendeif and Claude Lecomte*

Computing details

Data collection: APEX3 [START_REF] Bruker | APEX3, SADABS and SAINT[END_REF]; cell refinement: SAINT [START_REF] Bruker | APEX3, SADABS and SAINT[END_REF]; data reduction: SAINT [START_REF] Bruker | APEX3, SADABS and SAINT[END_REF]; program(s) used to solve structure: SHELXT (Sheldrick, 2018); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2018); molecular graphics: ORTEP-3 [START_REF] Farrugia | [END_REF]; software used to prepare material for publication: publCIF (Westrip, 2010).

(I)

Crystal data