(E)-3,4-Dihydroxybenzaldehyde 4-methylthiosemicarbazone

The title compound, C9H11N3O2S, adopts an E configuration with respect to the C=N bond. The molecule is approximately planar, with an r.m.s. deviation from the mean plane through all 15 non-H atoms of 0.152 Å; the dihedral angle between the benzene ring plane and the least-squares plane through the thiosemicarbazone unit is 12.48 (7)°. A weak intramolecular N—H⋯N interaction contributes to the planarity of the semicarbazone unit. Centrosymmetric pairs of O—H⋯O and N—H⋯S hydrogen bonds form chains along c, generating R 2 2(10) and R 2 2(8) ring motifs, respectively. In the crystal structure, these chains are further linked by intermolecular O—H⋯S and C—H⋯O interactions, forming stacks down the c axis.

The title compound, C 9 H 11 N 3 O 2 S, adopts an E configuration with respect to the C N bond. The molecule is approximately planar, with an r.m.s. deviation from the mean plane through all 15 non-H atoms of 0.152 Å ; the dihedral angle between the benzene ring plane and the least-squares plane through the thiosemicarbazone unit is 12.48 (7) . A weak intramolecular N-HÁ Á ÁN interaction contributes to the planarity of the semicarbazone unit. Centrosymmetric pairs of O-HÁ Á ÁO and N-HÁ Á ÁS hydrogen bonds form chains along c, generating R 2 2 (10) and R 2 2 (8) ring motifs, respectively. In the crystal structure, these chains are further linked by intermolecular O-HÁ Á ÁS and C-HÁ Á ÁO interactions, forming stacks down the c axis.

Comment
Thiosemicarbazones are a class of compounds that have been extensively investigated because of their biological activity (de Sousa et al., 2007). As a continuation of our work on thiosemicarbazone compounds as potential ligands in transition metal chemistry (Kayed et al., 2008;Tan et al., 2008a,b) we report here the structure of the title compound, (I).
The molecule of (I) (Fig. 1) is approximately planar with a dihedral angle of 12.48 (7)° between the phenyl ring plane and the least squares plane through the C7/N1/N2/C8/S2/N3 thiosemicarbazone moiety. The planarity of this section of the molecule is aided by a weak intramolecular N3-H3N···N1 interaction. The molecule adopts an E configuration with respect to the C═N bond and bond distances are normal (Allen et al., 1987).

Experimental
A 1:1 mixture of 3,4-dihydroxybenzaldehyde and N-methylhydrazinecarbothioamide was heated under reflux in ethanol for 2 hours. The solid product which separated upon cooling was filtered and recrystallised from methanol to afford colourless blocks of (I) in 54% yield (m.p. 418-419 K).

Refinement
The H atoms bound to N and O atoms were located in a difference electron density map and refined freely with U iso = 1.2U eq (N) and U iso = 1.5U eq (O). All other H-atoms were refined using a riding model with d(C-H) = 0.95 Å, U iso = 1.2U eq (C) for aryl and 0.98 Å, U iso = 1.5U eq (C) for methyl H atoms. Fig. 1. The structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms. An intramolecular hydrogen bond is drawn as a dashed line.  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 Rfactors(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