N,N′-[4,4′-Methylenebis(4,1-phenylene)]bis(2,6-difluorobenzamide)

The complete molecule of the title compound, C27H18F4N2O2, is generated by crystallographic twofold symmetry, with one C atom lying on the rotation axis. The dihedral angle between fluoro-substituted phenyl ring and the adjacent benzene ring is 10.37 (5)°. In the crystal, molecules are connected by N—H⋯O and C—H⋯F hydrogen bonds, resulting in supramolecular chains propagating along the c direction.


Experimental
In a round bottom flask, 25ml of tetrahydrofuran (THF) was mixed with 4,4'-diaminodiphenylmethane (0.01 mol,2 g) with stirring. Drops of 2,6-Difluorobenzylchloride (0.02 mol, 3.4 g ) which was dissolved in THF was then added. The mixture was refluxed for 30 min and the yellow precipitate formed was filtered and washed with alkaline water, then with toluene and further washed with dilute hydrochloric acid. The precipate was dissolved in methanol at room temperature yielding colourless plates of (I).

Refinement
Atom H1N1 was located from a difference Fourier maps and refined freely [N-H = 0.842 (15) Å]. The remaining H atoms were positioned geometrically [C-H = 0.95-0.9601 Å] and were refined using a riding model, with U iso (H) = 1.2 U eq (C).
The highest residual electron density peak is located at 0.61 Å from C6 and the deepest hole 0.64 Å located at from C1.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.