3,4-Dihydroxy-N′-(2-hydroxybenzylidene)benzohydrazide–methanol–water (2/1/3)

The asymmetric unit of the title compound, C14H12N2O4·0.5CH4O·1.5H2O, consists of two Schiff base molecules, three water molecules and one methanol molecule. The dihedral angle between the two benzene rings is 7.8 (2)° in one of the molecules and 4.0 (2)° in the other. Intramolecular O—H⋯O and O—H⋯N hydrogen bonds are observed. Molecules are linked into a three-dimensional network by O—H⋯O and N—H⋯O intermolecular hydrogen bonds.

The asymmetric unit of the title compound consists of two Schiff base molecules, three water molecules and one methanol molecule (Fig. 1). The corresponding bond lengths and angles in the two Schiff base molecules are nearly identical. The dihedral angle between the C1-C6 and C9-C14 benzene rings is 7.8 (2)° and that between the C15-C20 and C23-C28 benzene rings is 4.0 (2)°. The structure of each molecule is stabilized by O-H···O and O-H···N intramolecular hydrogen bonds.
In the crystal structure, the molecules are linked through intermolecular O-H···O and N-H···O hydrogen bonds (Table   1), forming a three-dimensional network (Fig. 2).

Experimental
Salicylaldehyde (1.0 mmol, 122.1 mg) and 3,4-dihydroxybenzoic acid hydrazide (1.0 mmol, 168.2 mg) were dissolved in a methanol solution (70 ml). The mixture was stirred at room temperature for 1 h and filtered. After keeping the filtrate in air for a week, yellow block-shaped crystals were formed.

Data collection
Bruker SMART CCD area-detector diffractometer 6429 independent reflections

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 > 2sigma(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.