Structural study of cadmium hydroxide suifates. VI. The layer structure of Cd 4 SO 4 (OH) 6 .1.5H 2 O studied from X-ray powder and single-crystal diffraction data D. Louer 0 Laboratoire de Chimie du Solide et Inorganique Moleculaire (UMR CNRS 6511), Institut de Chimie, Universite de Rennes, Avenue du General Leclerc, 35042 Rennes Cedex, France J. Rius Institut de Ciencia de Materials de Barcelona (CSIC), Campus de la UAB, 08193 Cerdanyola, Catalunya, Spain P. Benard-Rocherulle and M. Louer Laboratoire de Chimie du Solide et Inorganique Moleculaire (UMR CNRS 6511), Institut de Chimie, Universite de Rennes, Avenue du General Leclerc, 35042 Rennes Cedex, France (Received 6 December 2000; accepted 23 February 2001) The crystal structure of the layered cadmium hydroxide sulfate Cd 4 SO 4 (OH) 6 .1.5H 2 O has been solved from X-ray powder diffraction data. The compound crystallizes with hexagonal symmetry, a = 9.145(l) A, c= 15.099(3) A, V= 1093.5 A 3 , Z = 4 , space group P 6 3 . Due to the unusual environment of one cadmium atom and to the fact that a suitable thin tabular crystal could be found later, a single-crystal X-ray diffraction experiment was also carried out. In both cases the structure was solved applying direct-methods. The refinements converged to the residual factors R wp = 0.152 and R F = 0.059 from the powder data and /?, =0.058 and wR = 0.165 for the single crystal data case. The structure is built from brucite-type layers based on CdO 6 octahedra, in which one-seventh of the octahedral sites are empty. Directly above and below these empty sites, two additional octahedrically coordinated Cd atoms are located. The crystal chemistry of the cadmium hydroxide sulfate family is discussed. © 2001 International Centre for Diffraction Data. [DOI: 10.1154/1.1365125] I. INTRODUCTION At present a few cadmium hydroxide suifates are known, which have been clearly identified from the indexing of their powder diffraction pattern (Walter-Levy et al, 1974). Five of them have their structures reported, i.e., a-Cd 2 (OH) 2 SO 4 (Louer et al, 1982b), /3-Cd 2 (OH) 2 SO 4 (Labarre et al, 1976a), y-Cd 2 (OH) 2 SO 4 (Labarre et al, 1976b), Cd 8 (OH) 12 (SO 4 ) 2 .H 2 O (Louer et al, 1982a) and Cd 3 M 2 (OH) 2 (SO 4 ) 3 .2H 2 O (M=Cs, K) (Louer and Louer, 1982). This variety of well-defined phases reflects the com- plexity of the crystal chemistry of this family of basic cad- mium suifates. Most members have three-dimensional struc- tural frameworks, even so some connections with the chemically related layered hydroxide /3-Cd(OH) 2 have been pointed out. Long ago, de Wolff (PDF file No. 16-0816, ICDD, 2000) reported the existence of a cadmium hydroxide sulfate with the stated chemical composition Cd 45 SO 4 (OH) 7 .xH 2 O and an indexed powder diffraction pattern [F 30 = 68(0.0119,37)]. However, the crystal structure remains, to our knowledge, unknown. In the course of syn- thesis of new cadmium sulfate derivatives, crystals of a cad- mium hydroxide sulfate with the chemical formula Cd 4 SO 4 (OH) 6 .1.5H 2 O, as derived from the present study, and with a powder pattern closely related to that of the com- pound reported by de Wolff were obtained. Initial attempts to solve its crystal structure from single-crystal diffraction experiments failed, surely due to the extremely thin platy morphology of the crystals. Hence, the structure analysis was performed from X-ray powder data taking advantage of the noteworthy advances that have occurred for ab initio struc- a) Electronic mail: daniel.louer@univ-rennesl.fr ture determination (Langford and Louer, 1996). Although the overall structure model has been found from the powder data, the unusual surrounding of one cadmium atom, which could originate from insufficiently precise powder diffraction data, has justified new efforts to obtain single-crystal data to confirm the observations. This last investigation has ben- efited from recent progress in diffraction data collection with the new CCD area detectors. The present study deals with the structure investigation of Cd 4 SO 4 (OH) 6 .1.5H 2 O using both powder and single-crystal diffraction data. II. EXPERIMENTAL A. Material preparation and scanning electron microscopy analysis Crystals of cadmium hydroxide sulfate were produced at room temperature from an interdiffusion method in aqueous media (de Haan, 1963). By means of a pipette, a 1 M solu- tion of cadmium sulfate was introduced into a glass container which was three-quarters full of distilled water. The con- tainer was connected to a similar one filled with 2 M ammo- nia. After a few days, crystals having an extremely thin platelet shape were deposited on the walls of the first con- tainer. The crystals were washed with water and dried at 40 °C. Scanning electron microscopy (SEM) observations were carried out by means of a JEOL SEM 6301 F instru- ment. Two micrographs are shown in Figure 1, where platy crystals can be seen, as well as many defects in the stacking of the thin layers. The defective nature of the crystals can explain the difficulties encountered in previous attempts to solve the structure from single crystals. Moreover, some- 86 Powder Diffraction 16 (2), June 2001 0885-7156/2001/16(2)/86/6/$18.00 © 2001 JCPDS-ICDD 86