N,N′-(2,2′-Dithiodi-o-phenylene)bis(furan-2-carboxamide)

The reaction of 2,2′-dithiobis(benzenamine) with furan-2-carbonyl chloride produced the bis-amide title compound, C22H16N2O4S2, which, in the crystal, formed a helix; the structure consists of two planar furanoylbenzenamines related by an improper rotation of 96.3° about the S—S bond. The N-furanoylbenzenamine units are planar (maximum deviations = 0.316 and 0.132 Å). Each electron-deficient acylfuran stacks (centroid–centroid separations of the two pairs of π–π stacked aromatic rings are 3.918 and 3.953 Å) with the electron-rich benzenamine of the other N-furanoylbenzenamine unit, leading to a spiral structure. The conformation is stabilized by two bifurcated intramolecular N—H⋯(O,S) interactions.

The reaction of 2,2 0 -dithiobis(benzenamine) with furan-2carbonyl chloride produced the bis-amide title compound, C 22 H 16 N 2 O 4 S 2 , which, in the crystal, formed a helix; the structure consists of two planar furanoylbenzenamines related by an improper rotation of 96.3 about the S-S bond. The Nfuranoylbenzenamine units are planar (maximum deviations = 0.316 and 0.132 Å ). Each electron-deficient acylfuran stacks (centroid-centroid separations of the two pairs ofstacked aromatic rings are 3.918 and 3.953 Å ) with the electron-rich benzenamine of the other N-furanoylbenzenamine unit, leading to a spiral structure. The conformation is stabilized by two bifurcated intramolecular N-HÁ Á Á(O,S) interactions.

D-HÁ
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WW2132).
The structure ( Figure 1) proved to be of considerable interest in adopting a helical structure, the formation of which is driven, we suggest, by the interaction of the furan and benzene units, through space. A furan ring system is normally considered electron-rich, but in this case, carrying a 2-carboxamide unit, it is electron-deficient. The benzene rings, on the other hand, each with a sulfur and a nitrogen substituent, are electron-rich, compared with an unsubstituted benzene. We suggest that interaction of these electronically opposed π-systems, through space, orients the molecule in a helix such that one acyl-furan stacks above the electron-rich benzene located at the other end of the molecule, and the other acyl-furan stacks below the other benzene ring. The second diagram, Figure 2, is a view along the S-S bond. It clearly shows the helical nature of the molecule: the molecule shown has an anticlockwise sense of twist.
The extent to which the reference plane 1 and the three planes of the other 'half' of the molecule are not parallel is small.
Quantitatively, this can be measured by the dihedral angles between plane 1 and other three planes: 1 versus 2 = 23.05°; 1 versus 3 = 8.78°; 1 versus 4 = 6.45°. Thus, to a close approximation, the molecule consists of two units (one planar and one close to planar) which are nearly parallel, the largest deviation from which being 23.05° (between the two benzene rings: the extent to which the planes of these can be parallel is constrained by their attachment to the disulfide unit). At the closest points, the distances between the two pairs of stacked furan and benzene aromatic rings are 2.35Å and 3.56Å.

Refinement
The structure was solved by direct methods. The non-hydrogen atoms were refined anisotropically. H atoms were included in calculated positions with C-H lengths of 0.95(CH), 0.99(CH 2 ) & 0.98(CH 3 )Å; U iso (H) values were fixed at 1.2U eq (C) except for CH 3 where it was 1.5U eq (C). Fig. 1. View of (I) (50% probability displacement ellipsoids).   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.