2,2′-(Disulfanediyl)bis[4,6-(4-fluorophenyl)pyrimidine]

The title compound, C32H18F4N4S2, is a disulfide symmetrically substituted with two diaza-meta-terphenyl groups. In the crystal, the molecule adopts a twisted conformation with a C—S—S—C torsion angle of −91.82 (7)°. One of the 4,6-(4-fluorophenyl)pyrimidine groups is virtually planar, with dihedral angles between the pyrimidine and benzene groups of 4.00 (8) and 5.44 (8)°, wheares the other is non-planar with analogues dihedral angles of 18.69 (8) and 26.60 (8)°. The planar 4,6-(4-fluorophenyl)pyrimidine groups are involved in π–π stacking interactions via their 4-fluorophenyl groups [centroid–centroid distances of 3.8556 (11) and 3.9284 (11) Å] that assemble the molecules into columns extended along the a axis. In addition, the structure is stabilized by C—F⋯π [F⋯centroid = 3.4017 (16) Å], C—H⋯F and C—H⋯π interactions.


Comment
In view of the biological importance of pyrimidines and in continuation of our work on the synthesis of various derivatives of 4,4'-difluorochalcone (Samshuddin et al., 2011;Fun et al., 2010;Jasinski et al., 2010;Baktır et al., 2011), we have treated the 4,4'-difluorochalcone with thiourea. Instead of obtaining the expected thio pyrimidine, its dimerization product was obtained whose molecular and crystal structure is reported herein.
The S-S bond length was found at 2.0156 (6) Å and the S-S-C ar bond angles were measured at 104.74 (6)° and 105.41 (5).
These metrical parameters are in good agreement with values observed for comparable structures whose crystallographic data has been deposited with the Cambridge Structural Database (Allen, 2002): for 311 comparable structures, a distance range of 2.007-2.237 Å (e.s.d. = 0.021 Å) and an angle range of 96.89-107.54 ° (e.s.d. = 2.1 °) is apparent. The least-squares planes defined by the carbon atoms of the para-fluorophenyl groups enclose angles of 4.00 (8)° and 5.44 (8)° as well as 18.69 (8)° and 26.60 (8)°, respectively, with the plane of the aromatic moiety they are bonded to ( Fig. 1-3).
In the crystal, C-H···F contacts can be observed whose range falls by more than 0.1 Å below the sum of van der Waals radii of the H and F atoms. These are supported by one of the hydrogen atoms of a para-fluorophenyl moiety and connect the molecules to chains along [1 -1 -1]. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), these contacts necessitate a C(17) descriptor on the unitary level. In addition, there are C-H···π as well as C-F···π interactions ( Table 1).
The packing of the title compound in the crystal structure is shown in Figure 5.

Experimental
A mixture of 4,4'-difluorochalcone (2.44 g, 0.01 mol) and thiourea (0.76 g, 0.01 mol) was refluxed for 22 h in 25 ml of ethanolic KOH solution. The reaction mixture was cooled to room temperature and kept overnight. The solid product obtained on acidification with acetic acid was filtered and recrystallized from ethanol to obtain a yellow crystalline solid (yield: 51%). Single crystals suitable for the X-ray diffraction study were grown from DMF by slow evaporation at room temperature.