5-(4-Fluorophenyl)-2-[2-(5-phenyl-1,3-oxazol-2-yl)phenyl]-1,3-oxazole

In the title compound, C24H15FN2O2, the dihedral angles between the central benzene ring and the oxazole rings are 10.7 (6) and 64.1 (5)°. The dihedral angles between the oxazole rings and their pendant rings are 2.0 (3) and 24.3 (2)°. The F atoms are disordered over two sites with occupancies of 0.627 (3) and 0.373 (3) in the phenylene–oxazolyl–phenyl and in oxazolyl–phenyl fragments, respectively. In the crystal structure, molecules are linked through a network of C—H⋯F and weak π–π stacking interactions.

In the title compound, C 24 H 15 FN 2 O 2 , the dihedral angles between the central benzene ring and the oxazole rings are 10.7 (6) and 64.1 (5) . The dihedral angles between the oxazole rings and their pendant rings are 2.0 (3) and 24.3 (2) . The F atoms are disordered over two sites with occupancies of 0.627 (3) and 0.373 (3) in the phenyleneoxazolyl-phenyl and in oxazolyl-phenyl fragments, respectively. In the crystal structure, molecules are linked through a network of C-HÁ Á ÁF and weakstacking interactions.

Comment
Derivatives of 1,2-bis-(5-phenyl-oxazol-2-yl)benzene (ortho-POPOP) belong to the class of organic molecules, which exhibit efficient fluorescence with abnormally high Stokes shift (Doroshenko, 1996(Doroshenko, , 1999(Doroshenko, , 2000b. These molecules are prospective for their practical application as fluorescent probes, labels and chemosensors (Doroshenko, 2002a). Presence of two bulky heterocyclic substituents in 1,2-positions of the ortho-POPOP central benzene ring results in a significant sterical hindrance. This hindrance is manifested by a prominent non-planarity of ortho-POPOPs both in the crystalline state (Doroshenko, 1994) and in solutions (Doroshenko, 1996(Doroshenko, , 2002a. All the already examined crystal structures of the orthoanalogs of POPOP are characterized by essentially different angles between the planes of the central phenylene and each of the attached heterocyclic rings. Thus, two quasi-planar fragments containing two and three aromatic or heteroaromatic rings could be defined for the ortho-POPOPs molecules in crystals (Doroshenko, 1994(Doroshenko, , 1997(Doroshenko, , 2000b(Doroshenko, , 2002b. The same arrangement is typical for the newly synthesized fluoro-substituted representative of this series (Fig. 1). The fluorine atom and the corresponding hydrogen are significantly disordered in the crystal structure over two sites with probabilities 0.627 (3) and 0.373 (3) and vice versa (Fig. 2). The title molecules are linked through a network of C-H···F hydrogen bonds (Tab. 1) and π-electron ring-π-electron ring interactions in the solid state (Fig. 3, Tab. 2).
The necessary precursors have been prepared from the commercially available chemicals by the following procedures: 4-F-ω-Br-Acetophenone: 16 g (0.1 mol) of bromine was added dropwise to the solution 13.8 g (0.1 mol) of 4-F-acetophenone in 50 ml of ethanol at 30-40°C while stirring. After decolorization of the reaction mixture, ethanol was removed in vacuo. The resulting light yellow oily liquid was washed several times with distilled water to remove the traces of hydrobromic acid and used in the following synthesis without additional purification. Yield 19.1 g (0.088 mol, 88%). 4-F-ω-Amino-acetophenone hydrochloride: 6.5 g (0.046 mol) of hexamethylenetetramine was added portionwise at continuous stirring to the solution of 10 g (0.046 mol) of 4-F-ω-Br-acetophenone in 70 ml of chloroform. The reaction mixture supplementary materials sup-2 was stirred during 5 h, then the precipitated solid was filtered, washed with chloroform, dried and mixed with 25 ml of concentrated HCl in 70 ml of ethanol. The mixture was stirred until the complete dissolution was reached and then it was kept for 7 h at room temperature. The precipitated ammonium chloride was filtered off, the filtrate was concentrated in vacuo and the resulted solid was boiled with 50 ml of acetone during 1 h, cooled to the room temperature and filtered off to give 7.2 g (0.038 mol, 83%) of colorless powder of 4-F-ω-aminoacetophenone hydrochloride (m.p. 169-171°C).

Refinement
All the H atoms could be seen in the difference density maps with the exception of the atoms H2X and H27X that are disordered with F1 and F1A, respectively. However, the H atoms have been situated into the idealized positions with C-H = 0.93 Å and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C). The distances C2-F1 and C27-F1A have been restrained by SADI command of SHELXL97 (Sheldrick, 2008). The value of an effective standard deviation of SADI was 0.001. The sum of the occupations of F1 and F1A was constrained to equal to 1 as it follows from the reaction (Fig.   3). Both fluorines were refined anisotropically. Fig. 1. Two quasi-planar fragments in the molecule of the title compound in the crystalline state: phenylene-oxazolyl-phenyl mean plane is shown in red, while as oxazolyl-phenyl onein green (the interplanar angle is ~75°). Fig. 2. The title molecule with the atom numbering scheme. The displacement ellipsoids are drawn at the 25% probability level. Cg1, Cg2 and Cg3 denote the ring centroids. Fig. 3. The arrangement of the molecules in the crystal structure, viewed approximately along the c axis. The C-H···F interactions are represented by the dashed lines and the π-electron ring-π-electron ring interactions by the dotted lines. The H atoms not involved in interactions have been omitted [symmetry codes: (i) x + 1, y + 1, z; (ii) x + 1, y, z; (iii) -x, -y, -z; (iv) -x, -y + 1, -z.] Fig. 4. The scheme of the synthesis of the title compound. General procedure is analogous to that of Doroshenko (1994Doroshenko ( , 2000bDoroshenko ( , 2002b.

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.
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 Rfactors(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.