The crystal and molecular structure of cadmium( II) NN-diethyldithiocarbamate has been determined from threedimensional X-ray data and refined by anisotropic least-squares methods to a final R value of 0.084. Crystals are monoclinic, space group P2Jc. with a = 10.1 66, b = 10.746, c = 16.71 7 A, 13 = 11 1" 53'. In the solid state the complex is binuclear, the two halves of the molecule being related by a centre of symmetry, and should be formulated as [Cd2(S2CNEt2)4]. Two of the four NN-diethyldithiocarbamate groups act as bridging ligands, giving rise to a puckered eight-membered ring which comprises two cadmium, four sulphur, and two carbon atoms. The two symmetry-related cadmium atoms are five-co-ordinate, the co-ordination polyhedron being intermediate between a tetragonal pyramid and a trigonal bipyramid. The five cadmium-sulphur bond distances range from 2.536 to 2.800 A.

INTEREST has recently been revived in tricyanomethane, CH(CN) 3, and related compounds1-*. Salts of MnII, FeII, CoII, NiII, and CuII have been prepared and some of their properties investigated.7 On the basis of their electronic and infrared spectra a polymeric model for their structure has been proposed by Enemark and Holm7. Doubt remains, however, as to whether or not water is present in some of these salts. Enemark and Holm state that FeII and CoII tricyanomethanides retain half a molecule of water per metal atom, that the NiII compound can be prepared with a variable amount of water, and that the MnII and CuII salts retain one fourth of a molecule of water. On the other hand, the model proposed by these same Authors for the structure of these compounds "does not take into account the small amounts of water present"'. It should also be noted that in a previous paper3 the MnII and CuII salts were stated to be anhydrous.In order to substantiate the proposed structure and to find how water, if any, is co-ordinated, the X-ray crystal structure of the copper salt, Cu[C-(CX) 3] 2, was determined. Additional experiments relating to the suspected presence of water were carried out by thermogravimetric and differential thermal analysis. Samples were prepared both according to the directions of Enemark and Holm7 and by diffusiong. Debye-Scherrer diffraction patterns of powdered crystals prepared by the two different methods are identical.Crystal data listed below were collected, and the three-dimensional X-ray analysis described was performed, using crystals prepared by diffusion. These are black, yellow when powdered, crystallize in the orthorombic system; a = 7.176 & 0.005,