Benzyl N-[ 1-( furan-2-yl ) ethylidene ] hydrazine-carbodithioate

Dithiocarbazate derivatives have been widely studied and have great potential biological activity as anticancer and antimicrobial drugs (Bharti et al., 2000) and in radiopharmaceutical applications (Boschi et al., 2003). This functional group is of particular interest because it is easily tuned by reaction with different aldehydes or ketones to give varied geometries for chelation to transition metals. In the structure of the title compound, (I), we were interested in studying the effect of introducing a furan ring to determine if it can also participate in chelation to a metal centre. The previously reported Cd complex of this ligand (Tarafder et al., 2002b) indicated that it only forms a bis-chelating bidentate ligand without O coordination. The biological activity of the compound and its analytical characterization have also been reported (Tarafder et al., 2002a).

The title compound, C 14 H 12 N 2 S 2 O, contains a dithiocarbazate group. The phenyl ring is disordered and perpendicular [dihedral angle of 48.0 (3) ] to the rest of the molecule, which is planar.

Comment
Dithiocarbazate derivatives have been widely studied and have great potential biological activity as anticancer and antimicrobial drugs (Bharti et al., 2000) and in radiopharmaceutical applications (Boschi et al., 2003). This functional group is of particular interest because it is easily tuned by reaction with different aldehydes or ketones to give varied geometries for chelation to transition metals. In the structure of the title compound, (I), we were interested in studying the effect of introducing a furan ring to determine if it can also participate in chelation to a metal centre. The previously reported Cd II complex of this ligand (Tarafder et al., 2002b) indicated that it only forms a bis-chelating bidentate ligand without O coordination. The biological activity of the compound and its analytical characterization have also been reported (Tarafder et al., 2002a). Compound (I) (Figs. 1-3) crystallizes in the unprotonated thione form with a C S bond length of 1.664 (2) Å , which is slightly longer than that previously reported for a dithiocarbazate Schiff base [1.6503 (17) Å ; Chan et al., 2003]. This is in accordance with other experimental characterizations, which indicate that this type of compound forms the thione tautomer in the solid state. The formation of the Cd II complex occurs through coordination at the azomethane N atom and thiolate S atom (Tarafder et al., 2002b) but does not show any bond-length change: N1-N2 = 1.381 (2) Å in (I).
The molecule crystallizes in the conformer in which the N1-N2 bond adopts a trans geometry with respect to C12 S2, while the S-benzyl group adopts a cis geometry. The furan and phenyl groups are cis to each other across N2/N1/ C12/S1. The C13 N2 bond [1.289 (3) Å ] is formed from the condensation reaction. The C14 methyl group is cis to the furyl O atom in this free ligand but transforms to trans upon chelation to Cd II (Tarafder et al., 2002b), even though the O atom does not coordinate to the metal centre. The S1-C12 S2 angle is maintained at 125.22 (12) after coordination [125.22 (12) in (I)].

Experimental
The Schiff base ligand was prepared according to the literature method of Tarafder et al. (2002a). S-Benzyldithiocarbazate (1.98 g, 0.1 mol) in absolute ethanol (40 ml) was added to an equimolar quantity of 2-furylmethylketone in absolute ethanol (50 ml). The mixture was heated over a steam bath for 10 min and then cooled to 273 K in an ice bath. The Schiff base which precipitated was filtered, washed with cold ethanol and dried in vacuo over silica gel, giving a dark-orange product (yield 80%, m.p 406 K). Yellow single crystals of (I), suitable for X-ray analysis, were obtained by slow evaporation of an ethanol solution over a period of three weeks.  Table 1 Selected geometric parameters (Å , ).

Figure 2
A projection along the a axis of part of the packing of (I), showing that the phenyl groups form a layer in the crystal structure. The alternative orientations of the phenyl C atoms are coloured red and blue.

Figure 3
A projection along the b axis of a section of the crystal structure of (I). The alternative orientations of the phenyl C atoms are coloured red and blue. Note that if alternate red and blue phenyl groups are selected in any layer, there are no short intermolecular clashes. occupancy factors for the two orientations refined to 0.508 (4):0.492 (4), in close agreement with the value of 0.5:0.5 which would be required by strict alternation of the two orientations in each molecular layer (Figs. 2 and 3). All H atoms (including those of the disordered phenyl group) were located in a difference map, but those attached to C atoms were repositioned geometrically. All H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-98 and N-H = 0.85 Å ) and isotropic atomic displacement parameters [U iso (H) in the range 1.2-1.5 times U eq of the parent atom], after which they were refined with riding constraints.
KTJ gratefully acknowledges MOSTI, Malaysia, for an attachment grant under an NSF scholarship, and the Chemical Crystallography Laboratory, University of Oxford, for instrumental facilities.