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C8H9N3OS, monoclinic, C2/c, a = 14.206 (3), b = 14.244 (4), c = 10.457 (4) A, beta = 116.18(2) degrees, V = 1898.9 (8) A3, Z = 8, Dm = 1.387, D chi = 1.366 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 2.90 cm-1, F(000) = 816.0, T = 298 K, final R = 0.0429 for 1322 observed reflections. The S and hydrazinic N atoms lie trans. The lowering of antibacterial activity compared to that of 4-phenylthiosemicarbazide may be correlated with the decrease in negative charge on the hydrazinic N atom. The crystal structure is stabilized by hydrogen bonding, stacking interactions and van der Waals forces.

The crystal structure of 4-(4-chlorophenyl)thiosemicarbatide has been determined by direct methods. This p-chloro-substituted 4-phenylthiosemicarbazide, with greater antibacterial activity than its unsubstituted precursor, crystallises in the space group P2, / c with a = 14.594(4), b = 10.495(5), c = 12.384(4) A,The structure has been refined using 1 967 reflections with 1 2 3a(/). The antibacterial activity of both the present compound and its precursor has been attributed to electron delocalisation in the thiosemicarbazide moiety enhancing both its donor and reductive capacities.= 104.73(2)", 2 = 8,D, = 1 A69 g cm-=, and p(Mo-K,) = 5.83 cm With the recognition of the fact that many functionally important biomolecules contain S-N donor sites in suitable positions and the discovery of the antibacterial, antiviral, and antitumour properties of various thiosemicarbazides, thiosemicarbazones, and their metal complexes,' interest in the study of the chemical, biochemical, and structural aspects of these compounds and their derivatives is growing. The biological activity is, in general, believed to originate from metalcomplexing ' and reductive capacities of these organic ligands.Thiosemicarbazides, containing both hard (N) and soft (S) donors4 in positions suitable for chelating metal ions, have been shown to act as versatile complexing agents for various metal ions in different oxidation states. It has also been found that the antibacterial activities in uiiro of different substituted phenylthiosemicarbazides and their metal complexes vary with the nature of the substituent in the phenyl ring.' It is to be expected that the para-substitution of a chlorine atom, having a + R effect, in the phenyl ring of Cphenylthiosemicarbazide will make the thiosemicarbazide chain more electron rich in comparison with the corresponding chain in Cphenylthiosemicarbazide (2). The crystal structure of C(4-chloro-pheny1)thiosemicarbazide (1) was determined with the aim of correlating its structure and that of the previously reported 4phenylthiosemicarbazide (2) with their biological activities and to account for the greater activity of the chlorine-substituted compound (1). ExperimentalThe compound, obtained in powder form, was recrystallised from ethanol. Crystal Data.--C7H8ClN3S, M = 201.68,~ = 14.594(4), b = 10.495(5), c = 12.384(4) A, = 104.73(2)", V = 1 834(2) A-3, D, = 1.46 g ~m -~, F(OO0) = 832, p(Mo-K,) = 5.83 cm-', space group P2,/c, Z = 8 (two molecules in the asymmetric unit).The data were collected on an Enraf-Nonius CAD-4 diffractometer with graphite-monochromated radiation in the range 2" < 8 < 25". 1967 out of the 3 422 unique reflections measured were considered to be observed [ I 2 3a(I)J. The intensities were corrected for Lorentz and polarisation effects but not for absorption.

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