[2,7-Diethoxy-8-(4-fluorobenzoyl)naphthalen-1-yl](4-fluorophenyl)methanone

In the molecule of the title compound, C28H22F2O4, the benzoyl groups are aligned almost antiparallel and the fluorobenzene rings form a dihedral angle of 14.12 (7)°. The dihedral angles between the 2,7-diethoxynaphthalene ring system and the benzene rings are 70.00 (4) and 67.28 (4)°. In the crystal, molecules are linked by C—H⋯O and C—H⋯F hydrogen bonds, forming layers parallel to the ab plane. The layers are further connected by π–π interactions [centroid–centroid distances of 3.6115 (10) Å] into a three-dimensional structure.


Related literature
As a part of our continuous studies on the molecular structures of this kind of homologous molecules, the X-ray crystal structure of the title compound, 1,8-bis(4-fluorobenzoyl)-2,7-diethoxynaphthalene is discussed in this article.
In the molecule (Fig. 1), two aroyl groups are non-coplanarly attached to the naphthalene ring and are oriented in opposite direction. The dihedral angles between the planes of the benzene rings [C12-C17 and C19-C24] and the naphthalene ring system (C1-C10) are 70.00 (4)° and 67.28 (4)°, respectively. Besides, the dihedral angle between the benzene rings is 14.12 (7)°.
The molecular packing of the title compound is mainly stabilized by dual C-H···O hydrogen bonds between the benzene rings and the ketonic carbonyl groups along the a axis (C16-H16···O1 i =2.30 Å and C23-H23···O2 ii =2.37 Å; Table 1 and Fig. 2) and by C-H···F hydrogen bonds between the naphthalene rings and the fluorine atoms on the benzene rings (C6-H6···F1 iii =2.44 Å; Table 1 and Fig. 3), resulting in the formation of molecular layers parallel to the ab plane. In addition, the layers interact through π-π interactions with centroid-centroid distances of 3.6115 (10) Å to form a three-dimensional structure. The above mentioned results suggest that the title compound has similarities with 1,8-dibenzoyl-2,7-diethoxynaphthalene (Isogai et al., 2013) in the dihedral angles between the benzene rings and the naphthalene ring and the distance of the C-H···O hydrogen bond between the benzene ring and the ketonic carbonyl group.

Experimental
To a 50 ml flask, 2,7-diethoxynaphthalene (2.0 mmol, 489 mg), 4-fluorobenzoic acid (5.6 mmol, 785 mg), and phosphorus pentoxide-methanesulfonic acid (8.8 ml) were placed. The reaction mixture was stirred at 60°C for 1.5 h. After the reaction, the mixture was poured into ice-cold water and extracted with 25 ml of CHCl 3 for three times. The combined extracts were washed with water, and 2 M aqueous NaOH followed by washing with brine. The organic layers thus obtained were dried over anhydrous MgSO 4 . The solvent was removed under reduced pressure to give cake. The crude product was purified by reprecipitation (CHCl 3 /methanol; isolated yield 91%). Furthermore, the isolated product was crystallized from CHCl 3 to give single-crystal suitable for X-ray analysis, m.p. 482.7-483.3 K.

Refinement
All H atoms were located in a difference Fourier map and were subsequently refined as riding atoms, with C-H = 0.95 (aromatic), 0.98 (methyl) and 0.99 (methylene) Å, and with U iso (H) = 1.2U eq (C). The positions of methyl H atoms were rotationally optimized.   A partial view of the crystal packing of the title compound, showing the intermolecular C-H···O hydrogen bonds (see Table 1 for details; symmetry codes: (i) -1 + x, y, z; (ii) 1 + x, y, z).  A partial view of the crystal packing of the title compound, showing the intermolecular C-H···F hydrogen bonds (see Table 1 for details; symmetry codes: (iii) 1/2 -x, 1/2 + y, 1/2 -z).

[2,7-Diethoxy-8-(4-fluorobenzoyl)naphthalen-1-yl](4-fluorophenyl)methanone
Crystal data Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained w = 1/[σ 2 (F o 2 ) + (0.0756P) 2 + 0.3064P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.20 e Å −3 Δρ min = −0.18 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.