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The crystal structure of thiosemicarbazide, previously determined from photographic data, has been redetermined using intensity data collected by means of a four-circle Picker diffractometer at room temperature. The analysis has been valuable in giving a direct determination of the hydrogen atom positions. The final R= 2.4%. Earlier hypotheses on the hydrogen bonding are confirmed.

Bisthiourea-zinc acetate, Zn[SC(NH2)2]2(CH3COO)2, is monoclinic, P21/c: a=6"938, b= 17"678, c= 11.798 A, ,8= 112.6 °, Z=4. The structure, solved by means of three-dimensional Fourier methods, has been refined with the use of the anisotropic differential synthesis. Zn coordinates to two S atoms from two thiourea molecules (Zn-S 2-326 and 2"261/~) and to two O atoms (Zn-O 1.973 and 1 "954/~k) from two acetate groups, to form a tetrahedral arrangement. Two further oxygen atoms from the same acetate groups are involved in weaker interactions with the metal atom at 2-996 and 2"891 ~; as a consequence of these interactions the planes of the acetate ions are oriented in such a way that the Zn atom almost lies within them. There are no significant differences between corresponding bond distances and angles in the two thiourea molecules: these are much the same as in the uncoordinated thiourea. IntroductionThiourea adducts with acetates of divalent metals have been prepared and described by Nardelli & Chierici (1959), who showed that the bisthiourea compounds of cobalt and zinc are isostructural. A three-dimensional X-ray analysis has now been carried out to study the coordination of the thiourea molecule and carboxyl group by the metal atom in these compounds. In particular, it seemed interesting to determine the role played by the oxygen atoms in the coordination and the influence, if any, of the sulphur-metal interaction on bond distances and angles in the thiourea molecule. ExperimentalThe unit-cell constants, remeasured on single-crystal rotation and Weissenberg photographs and refined by a least-squares procedure on powder diffractometer data (Cu Ka, 2= 1.5418 A), are as follows:Zn[SC(NH2)2]2(CH3COO)2; M= 335.7 a = 6.938 + 0.003, b = 17.678 _+ 0.006, c = 11.795 + 0.006 A fl=112°47'_+18'; v=1334A3; z=4; Dz=l.671, Dra = 1"61 g.cm -3 /z = 54.6 cm-X (Cu K~), F(000)= 632.Space group" P21/c (from systematic absences).Two series of equi-inclination Weissenberg photographs (filtered Cu radiation, multiple film technique) were taken at room temperature about [100] with levels h=0,1,... 6, and about [001] with levels l--0,1,... 10. 2128 independent reflexions were observed out of a possible 2554. The intensities were measured photometrically and corrected for Lorentz, polarization and spot shape effects. The sample used to take the photographs around [100] was a prism elongated along this axis and was considered as a cylinder with a mean radius of 0.008 cm in calculating the absorption correction; the photographs around [001] were taken with a nearly spherical fragment with a mean radius of 5719 (14) 2607 (4) 2286 (9) 38 (6) 57 (2) 41 (7) 1 (6) 14 (9) -12 (6) N (4) 8481 (11) 2110 (4) 2023 (7) 31 (5) 58 (2) 46 (7) 2 (5) 9 (8) -6 (6) C (1) 1930 ( (6) 247 (12) 3177 (3) 298 (9) 37 (7) 33 (1) 48 (8) 3 (5) 14 ( 3 7 5 9 8 26 4 6 9 11 96 41 14 50 19 oo 9 29 21 5 107 13 9 16 2 8 5 4 4 8 6 131 5 7 44 15 47 98 8 3 17 L. CAVALCA, G. FAVA GASPARRI, G. D. ANDREETTI AND P. DOMIANO 91 0.02 cm, and for th...

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