Acta Cryst. (2008). E64, o1790-o1791 [ doi:10.1107/S1600536808026305 ]
Abstract: The bis-Schiff base title compound, C20H16N2O4·C7H8, crystallized as a toluene solvate. In the solid state, it is present as its prototropic tautomer formed by transfer of one of the ortho-hydroxyl H atoms. The proton transfer is accompanied by a shift of electron pairs, as is evident from the observed C-O and C-N bond distances of 1.305 (2) and 1.315 (2) Å, which are largely consistent with C=O and C-N distances. The actual molecule present in the solid state is thus the charge-neutral -keto amine, with a small contribution of its zwitterionic valence tautomer via partial delocalization of electron pairs along the N-C-C-C-O atom chain. The dihedral angles between the central benzene ring and the two outer benzene rings of the Schiff base are 51.99 (8) and 12.95 (9)°. Intramolecular O-HN and N-HO hydrogen bonds generate S(6) ring motifs, whereas intramolecular N-HN hydrogen bonds generate S(5) ring motifs. In the crystal structure, O-HO hydrogen bonds and weak C-HO interactions link the molecules into one-dimensional zigzag chains along the b axis; these chains are further stacked by O-HO and weak C-HO interactions along the c axis, forming two-dimensional extended networks parallel to the bc plane. In addition, the crystal structure is further stabilized by weak C-H and - interactions.
Online 20 August 2008
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