Crystal structures of two hydrazinecarbothioamide derivatives: (E)-N-ethyl-2-[(4-oxo-4H-chromen-3-yl)methylidene]hydrazinecarbothioamide hemihydrate and (E)-2-[(4-chloro-2H-chromen-3-yl)methylidene]-N-phenylhydrazinecarbothioamide

The title compounds, (I) and (II), are hydrazinecarbothioamide derivatives. In the crystal of (I), two independent molecules are linked by bifurcated N—H⋯O and C—H⋯O hydrogen bonds, forming two (6) ring motifs, and (10) and (14) ring motifs. In the crystal of (II), molecules are linked by pairs of N—H⋯S hydrogen bonds, forming inversion dimers with an (8) ring motif.


Chemical context
Thiosemicarbazones belong to a large group of thiourea derivatives which are derived from parent aldehydes and ketones. The biological activity of these compounds depends on the parent aldehyde and ketone (Beraldo & Gambino, 2004). Derivatives of hydrazinecarbothioamide constitute an important group of multidentate ligands with potential binding sites available for a wide variety of metal ions. The chemistry of thiosemicarbazone complexes has received much attention owing to their significant biological activities and medicinal properties. Presently, the areas in which thiosemicarbazones are receiving the most attention are based on their antitumour, antiprotozoal, antibacterial and antiviral activities (Finch et al., 1999;Antholine et al., 1977). -Nheterocyclic thiosemicarbazones possess antitumour properties partially related to their ability to inhibit ribonucleoside reductase (RR), an iron-containing enzyme which is essential in DNA synthesis (Sartorelli et al., 1970). The medicinal action of these thiosemicarbazones appears to be directly related to their ability to chelate the iron atom of the active site of RR or by destroying the tyrosinase radical present in a subunit of this protein (Thelander & Graslund, 1983). The structures of the ISSN 2056-9890 title compounds were determined in order to investigate the extent of electron delocalization, ligand conformations and to illustrate their biological implications.

Structural commentary
In compound (I) (Fig. 1), the chromene moieties of molecules A and B are essentially planar, with maximum deviations of 0.028 (3) and 0.016 (3) Å for atoms C7 and C7 0 , respectively. However, in compound (II) (Fig. 2), the chromene moiety is not quite planar with a dihedral angle of 5.67 (12) between the mean planes of the fused six-membered rings. In compound (II), the pyran ring of the chromene moiety adopts a screw-boat conformation [puckering amplitudes and smallest displacement parameters are q = 0.314 (2) Å , = 116.4 (4) , ' = 147.5 (5) and ÁC 2 = 0.7 (3)]. In compound (II), the dihedral angle between the chromene moiety and the phenyl ring is 61.18 (9) . The deviation of the carbonyl O atoms (O2 and O2 0 ) from the mean plane of the pyran ring in compound (I) are 0.0838 (18) and 0.0386 (19) Å in molecules A and B, respectively, while the deviation of the Cl atom in compound (II) is 0.312 (1) Å .
The hydrazinecarbothioamide backbone is almost planar, with the maximum deviation being exhibited by atom N2 in both compounds; 0.025 (2) and 0.051 (2) Å , respectively, in molecules A and B of compound (I) and 0.072 (2) Å in compound (II).
Thiosemicarbazones exist in the thione form in the solid state and in solution they exist as an equilibrium mixture of thione and thiol forms (Kurup & Joseph, 2003). The fact that the compounds exists in the thione form is confirmed by the N-N, N-C and C S bond lengths.. The C-S bond lengths are 1.681 (2) and 1.673 (2) Å in molecules A and B, respectively, of compound (I), and 1.668 (2) Å in compound (II). These bond lengths are intermediate between normal S-Csp 2 single-bond and S Csp 2 double-bond distances of ca 1.75 and 1.59 Å , respectively, indicating the presence of partial doublebond character (Kumbhar et al., 1997). The N1-N2 bond lengths [varying between 1.367 (2) and 1.369 (2) Å ] are very close to that reported for a similar substituted hydrazinecarbothioamide compound (Joseph et al., 2004). The resonance involving the pyran ring would account for the shortening of the N-N distance through extensive delocalization. The C-N bond lengths [varying between 1.324 (3) and 1.361 (3) Å ] are shorter than the normal C-N single bond length (ca 1.48 Å ), also indicating some degree of delocalization in both compounds. The S1 C11-N2-N1 torsion angles are 177.31 (16) and 174.29 (16) , respectively, in molecules A and B of compound (I) and À172.62 (17) in compound (II). This indicates that the thionyl atom S1 is positioned trans to the azomethane nitrogen atom N1 in both compounds.

Supramolecular features
The water molecule of crystallization plays an important role in the hydrogen-bonding patterns of the three-dimensional network in compound (I). In the crystal packing of compound (I), bifurcated N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds involving carbonyl oxygens O2 and O2 0 in adjacent molecules, The molecular structure of the two independent molecules (A and B) of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The molecular structure of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Synthesis and crystallization
Compound (I): 1.19 g (0.01 mol) of N-ethylhydrazinecarbothioamide was dissolved in 20 ml of hot ethanol and to this was added 1.74 g (0.01 mol) of 4-oxo-4H-chromene-3-carbaldehyde in 10 cm 3 of ethanol over a period of 10 min with continuous stirring. The reaction mixture was refluxed for 2 h and allowed to cool whereby a shiny white compound began to separate; this was filtered and washed thoroughly with ethanol and then dried in vacuo. The compound was recrystallized from hot ethanol (yield: 96%), giving colourless block-like crystals.
Cg1 is the centroid of the C12-C17 phenyl ring. (3)  151 continuous stirring. The reaction mixture was refluxed for 2 h and allowed to cool whereby a shiny yellow compound began to separate. It was filtered and washed thoroughly with ethanol and then dried in vacuo. The compound was recrystallized from hot ethanol (yield: 89%), giving colourless blocklike crystals.

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 > σ(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.

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 > σ(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.