2-((E)-{2-[(E)-2,3-Dihydroxybenzylideneamino]-5-methylphenyl}iminiomethyl)-6-hydroxyphenolate

The asymmetric unit of the title Schiff base compound, C21H18N2O4, consists of four independent zwitterions (A, B, C and D) with similar conformations. In each independent molecule, the methyl group is disordered over two positions; the occupancies of the two positions are 0.819 (5) and 0.181 (5) in molecule A, 0.912 (5) and 0.088 (5) in B, 0.734 (5) and 0.266 (5) in C, and 0.940 (6) and 0.060 (6) in D. The dihydroxyphenyl and the hydroxyphenolate rings in molecule A form dihedral angles of 17.36 (12) and 13.30 (12)degrees, respectively, with the central benzene ring, whereas the respective angles for molecules B, C and D are 30.22 (11)/ 7.46 (11), 35.26 (12)/11.01 (12) and 39.89 (12)/4.29 (12)degrees. In all independent molecules, intramolecular N-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds generate S(6) ring motifs. The four independent molecules are linked into two pairs, viz. A-B and C-D, by intermolecular O-H center dot center dot center dot O hydrogen bonds. These pairs are linked into a two-dimensional network parallel to the ab plane by C-H center dot center dot center dot O hydrogen bonds. In addition, C-H center dot center dot center dot pi and pi-pi [centroid-centroid distance = 3.5153 (14)-3.7810 (15) A] interactions stabilize the crystal structure.