Zn compound" M r = 5 3 7 . 8 2 , monoclinic, P2Jc, a = 7.939 (2), b = 16. 120 (2), c = 7.691 (2)/~, fl = 99.87 (2) °, V = 969.7 A 3, Z = 2, O m = 1.83, D x -1.84 g cm -3, Mo Kt~, ~. = 0.71069 ~, g = 14.7 cm -~, F(000) = 552, T = 294 (2) K. Cd compound: M r = 584.85, monoclinic, P2Jc, a = 8.036 (2), b = 16.145(3), c = 7 . 8 7 0 ( 1 ) A , f l = 1 0 0 . 2 4 ( 1 ) °, V = 1004.8 ,~3, Z = 2, D m = 1.92, D x = 1.93 gcm -3, Mo K~t, 2 = 0.71069 ,~, g = 12.4 cm -l, F(000) = 588, T = 294 (2) K. R = 0 . 0 2 8 and 0.025 for 1581 and * Saccharin is 1,2-benzisothiazol-3 (2H)-one 1,1-dioxide. "t" To whom correspondence should be addressed. 1850 intensities, respectively. The isostructural pair of complexes have centrosymmetric trans octahedral geometry. Delocalization of the charge away from the N atom may explain the weakness of the M N bond. The structures of the Cd H and Zn ~ compounds are compared with those involving Mn H, Fe II, Co H, Ni x~ and Cu ~I and trends in the metal-ligand M--N, M--OH 2 bond lengths are discussed. Introduction. We have described the syntheses and properties of a series of complexes with general formula [M(C7H4NO3S)2(H20)4].2H20 ( M M n Ix, Fe II, Co n, Ni II, Cu II and Zn II) (Haider, Malik & Ahmed, 1981; 0108-2701/84/071147-04501.50 © 1984 International Union of Crystallography 1148 [Zn(CTH4NO3S)2(H20)4].2H20 AND [Cd(CTH4NOaS)2(H20)4].2H20 Haider & Malik, 1982) and reported the crystal structure analyses of the Fe, Co, Ni and Cu complexes (Ahmed, Habib, Haider, Malik & Hursthouse, 1981; Haider, Malik, Ahmed, Hess, Riffel & Hursthouse, 1983). While our work was in progress an independent structural report of the corresponding Mn complex appeared (Kamenar & Jovanovski, 1982). In the present paper, we describe the crystal structure determinations of the Zn and Cd derivatives and discuss the structural variations in all seven related complexes. Experimental. Zn complex (ZNSAC) prepared as described earlier (Haider & Malik, 1982). Cd complex (CDSAC) prepared by reacting cadmium chloride with Na-saccharin in aqueous medium (Haider, Malik, Hursthouse & Wadsten, 1984). D m by flotation. Crystals suitable for X-ray work obtained by recrystallization from water. Lattice parameters determined by least-squares refinement of setting angles for 25 reflections [16 < 8(Mo K0t) < 17°], automatically centred on Enraf-Nonius CAD-4 diffractometer; intensity data recorded on same instrument, MoK~t radiation (graphite monochromator), following procedures described earlier (Hursthouse, Jones, Malik & Wilkinson, 1979). Semi-empirical absorption corrections applied to both data sets, using ~-scan values for 3 reflections in each case. Merging equivalent reflections and omitting those with F o < 3a(Fo) yielded 1581 (ZNSAC) and 1850 (CDSAC) unique data, which were used in structure analyses. Further experimental information is given in Table 1. Structures solved by heavy-atom method and refined by least squares. All non-hydrogen atoms refined anisotropically, hydrogen atoms (located from difference maps) isotropically. In final stage of refinement empirical isotropic extinction parameter x varied in modified expression for calculated structure factor, F c' = F~(1 x Fc2/sin8), and weighting scheme based on w = 1/[a2(Fo) + gFo 2] applied. Refinement on F converged at R =0.0281 (ZNSAC) and 0.0246 (CDSAC), with d / a < 0.1, absolute values of peaks and troughs in final difference maps <0.3e/% -3. Calculations performed on DEC VAXll /750 computer using S H E L X 7 6 (Sheldrick, 1976). Neutral-atom scattering factors from Cromer & Mann (1968) and Stewart, Davidson & Simpson (1965) for non-H and H atoms, respectively. Final atomic parameters and the bond lengths and angles involving the non-H atoms are given in Tables 2 and 3, respectively.* * Lists of structure factors, anisotropic thermal parameters, coordinates, bond lengths and angles involving the saccharinato hydrogen atoms, hydrogen-bond dimensions and data related to least-squares plane and dihedral angle calculations have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 39313 (22 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. Table 1. Exper imenta l details