3,3′-Dibenzoyl-1,1′-dibenzyl-1,1′-(ethane-1,2-diyl)dithiourea

In the title compound, C32H30N4O2S2, the carbonyl and thiocarbonyl groups are found in a rare synclinal conformation, with an S—C⋯C—O pseudo-torsion angle of 62.6 (2)°. The molecule has Ci = S 2 point-group symmetry with a crystallographic center of inversion located in the middle of the ethylene bridge. One of the symmetry-independent phenyl rings is disordered over two orientations, with a site-occupation ratio of 70:30. The distances between the centroids of the nearest phenyl rings are equal to one of the lattice constants [a = 4.7767 (2) Å], so stacking interactions are extremely weak. Molecules are joined by bifurcated hydrogen bonds (N—H⋯O and N—H⋯S), forming a ladder-like arrangement along [100]. van der Waals forces combine these ladders into a three-dimensional structure. The dependency between the S⋯O distance and the improper S=C⋯C=O torsion angle based on 739 structures containing the CC(=O)NC(=S)N moiety is discussed.

In the title compound, C 32 H 30 N 4 O 2 S 2 , the carbonyl and thiocarbonyl groups are found in a rare synclinal conformation, with an S-CÁ Á ÁC-O pseudo-torsion angle of 62.6 (2) . The molecule has C i = S 2 point-group symmetry with a crystallographic center of inversion located in the middle of the ethylene bridge. One of the symmetry-independent phenyl rings is disordered over two orientations, with a siteoccupation ratio of 70:30. The distances between the centroids of the nearest phenyl rings are equal to one of the lattice constants [a = 4.7767 (2) Å ], so stacking interactions are extremely weak. Molecules are joined by bifurcated hydrogen bonds (N-HÁ Á ÁO and N-HÁ Á ÁS), forming a ladder-like arrangement along [100]. van der Waals forces combine these ladders into a three-dimensional structure. The dependency between the SÁ Á ÁO distance and the improper S CÁ Á ÁC O torsion angle based on 739 structures containing the CC( O)NC( S)N moiety is discussed.
Three main geometries of N-acylthioureas based on the S···O distance (d SO ) and the S=C···C=O improper torsion angle (φ SCCO ) can be distinguished: synperiplanar type (i) and (iii) with |φ SCCO | ≈ 0° as well as antiperiplanar type (ii) with | φ SCCO | ≈ 180° (Fig. 4). The S···O distance in type (i) is about 3 Å while in type (iii) is about 5 Å. Transition between type (i) and (ii) is smooth and is accomplished by rotation about the thioamide bond. Theoretical relation between d SO and φ SCCO assuming constant bond lengths and valence angles can be expressed as (see: solid line in Fig. 4): where A and B are calculated as: Numerical values of bond lengths and angles are the average ones calculated in Vista program on the basis of 739 structures (980 values) containing CC(=O)NC(=S)N moiety found in CSD 5.32 (Allen, 2002) Type (ii) is generally more stable than type (i) due to the formation of the intramolecular N-H···O hydrogen bond.
When there is no suitable hydrogen atom to form hydrogen bonds (N,N-disubstituted derivatives) the anticlinal geometry (|φ SCCO | ≈ 120°) is preferred. Only 58 out of 980 points in Fig. 4 represent type (i) with d SO < 4 Å and |φ SCCO | < 90°. In this type the S···O distance is slightly greater than theoretical value due to sulfur-oxygen repulsion. Molecules of type (iii) contain covalent six-membered rings (see: structure (iii) in Fig. 4) preventing any rotation, so there is no possibility to transform this type to any other.

Experimental
Synthesis was performed according to Douglass & Dains (1934): 2.50 g (33 mmol) of ammonium thiocyanate and 20 ml of acetone were placed in a two-necked flask. Through a dropping funnel 3.49 ml (30 mmol) of benzoyl chloride in 20 ml of acetone was added with stirring. After addition was completed the mixture was refluxed for additional 15 min and then 3.54 ml (15 mmol) of N,N′-dibenzylethane-1,2-diamine in 20 ml of acetone was added through the dropping funnel. The mixture was carefully poured to the 500 ml of water with stirring. The resulting precipitate was filtered on a Büchner funnel. The crude product was recrystallized from acetone. Colorless single crystals suitable for X-ray diffraction analysis were isolated with 72% yield. Melting point: 165 (1)°C.

Refinement
All C-bonded hydrogen atoms were placed in calculated positions (aromatic: d CH = 0.97 Å, methylene: d CH = 0.93 Å) and were treated as riding on their parent atoms with U iso (H) = 1.2 U eq (C). H1N atom was located from difference Fourier map and refined isotropically with d NH restrained to 0.88 (1) Å.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.
Symmetry code: (i) -x + 2, -y + 1, -z + 1.      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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (