(E)-N′-[2-(4-Chloro-3-nitrophenylsulfonyloxy)-3-methoxybenzylidene]isonicotinohydrazide acetic acid tetrasolvate

In the title compound, C20H15ClN4O7S·4CH3COOH, the central o-vanillin group makes dihedral angles of 9.50 (11) and 42.86 (7)°, respectively, with its attached pyridine and nitrobenzene rings. The crystal packing is stabilized by N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds and C—H⋯O interactions, leading to an infinite three-dimensional network. A short intramolecular C—H⋯O contact is also seen.

In the title compound, C 20 H 15 ClN 4 O 7 SÁ4CH 3 COOH, the central o-vanillin group makes dihedral angles of 9.50 (11) and 42.86 (7) , respectively, with its attached pyridine and nitrobenzene rings. The crystal packing is stabilized by N-HÁ Á ÁO, O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds and C-HÁ Á ÁO interactions, leading to an infinite three-dimensional network. A short intramolecular C-HÁ Á ÁO contact is also seen.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2646).
(E)-N'-[2-(4-Chloro-3-nitrophenylsulfonyloxy)-3-methoxybenzylidene]isonicotinohydrazide acetic acid tetrasolvate X.-L. Zhen and X.-L. Li Comment There has been a steady growth of interest in the synthesis, structure, and reactivity of Schiff bases due to their potential applications in areas such as biological modelling, catalysis, and molecular magnets (Jones et al., 1979;Larson & Pecoraro, 1991). One of the aims of investigating the structural chemistry of Schiff bases is to develop protein and enzyme mimics (Santos et al., 2001). As part of an investigation of the coordination properties of Schiff bases functioning as ligands, we report the synthesis and structure of the title compound (I).

Experimental
An anhydrous ethanol solution (50 ml) of 2-formyl-6-methoxyphenyl 4-chloro-3-nitrobenzenesulfonate (3.72 g, 10 mmol) was added to an anhydrous ethanol solution (50 ml) of isonicotinohydrazide (1.37 g, 10 mmol) and the mixture stirred at 350 K for 5 h under nitrogen, giving a yellow precipitate. The product was isolated, recrystallized from ethanol and then dried in a vacuum to give the pure compound in 78% yield. Yellow single crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of an acetic acid solution.

Refinement
The H atoms of the water molecule and imine group were located in difference maps and then treated as riding atoms. All other H atoms were included in calculated positions and refined using a riding model approximation.  Fig. 1. The structure of (I) with displacement ellipsoids for non-H atoms drawn at the 30% probability level.  as those based on F, and R-factors based on ALL data will be even larger.