2,2′-Bis{8-[(benzylamino)methylidene]-1,6-dihydroxy-5-isopropyl-3-methylnaphthalen-7(8H)-one}

The asymmetric unit of the title compound, C44H44N2O6, contains two independent molecules with similar conformations. The dihydronaphthalene ring systems are approximately planar [maximum deviations = 0.036 (2), 0.128 (2), 0.0.24 (2) and 0.075 (2) Å]. The dihedral angle between two dihydronaphthalene ring systems is 83.37 (4)° in one molecule and 88.99 (4)° in the other. The carbonyl O atom is linked with the adjacent hydroxy and imino groups via intramolecular O—H⋯O and N—H⋯O hydrogen bonds. In the crystal, molecules are linked through O—H⋯O hydrogen bonds into layers parallel to (001), and adjacent layers are further stacked by π–π interactions between dihydronaphthalene and phenyl rings into a three-dimensional supramolecular architecture. In the crystal, one of the isopropyl groups is disordered over two positions with an occupancy ratio of 0.684 (8):0.316 (8).

The asymmetric unit of the title compound, C 44 H 44 N 2 O 6 , contains two independent molecules with similar conformations. The dihydronaphthalene ring systems are approximately planar [maximum deviations = 0.036 (2), 0.128 (2), 0.0.24 (2) and 0.075 (2) Å ]. The dihedral angle between two dihydronaphthalene ring systems is 83.37 (4) in one molecule and 88.99 (4) in the other. The carbonyl O atom is linked with the adjacent hydroxy and imino groups via intramolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. In the crystal, molecules are linked through O-HÁ Á ÁO hydrogen bonds into layers parallel to (001), and adjacent layers are further stacked byinteractions between dihydronaphthalene and phenyl rings into a three-dimensional supramolecular architecture. In the crystal, one of the isopropyl groups is disordered over two positions with an occupancy ratio of 0.684 (8):0.316 (8).

Experimental
Gossypol was obtained from the Experimental Plant of the Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan where it was produced from by-products of the cottonseed oil industry. To prepare the Schiff base compound, gossypol was mixed with benzylamine in a 1:3 molar ratio in the acetone. This reaction solution was allowed to stand in the dark for 3 days, during which crystalline precipitate formed within solution. The precipitate was recovered by filtration and air-dried. Suitable crystals were selected from the precipitate and were used for diffraction without additional recrystallization.

Refinement
The H atoms attached to oxygen atoms were found from the difference Fourier maps and were refined isotropically, other H atoms were placed in geometrically idealized positions (N-H = 0.86, C-H = 0.93-0.96 Å, and treated as riding on their parent atoms with U iso (H) = 1.2U eq (C,N) and 1.5U eq (C). One of isopropyl group is disordered over two positions, occupancies were refined to 0.684 (8):0.316 (8).

Figure 1
The molecular structure of title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A packing diagram for title compound.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.  (