CRYSTAL-STRUCTURE AND TEMPERATURE-RESOLVED POWDER DIFFRACTOMETRY OF CD5(OH)8(NO3)2.2H2O

A new cadmium hydroxide nitrate Cd5(OH)8(NO3)2 · 2H2O was prepared by an interdiffusion method. It is monoclinic with the cell parameters a = 18.931(3) Å, b = 6.858(2) Å, c = 5.931(1) Å, β = 94.85(2)°; the space group is C2 m with Z = 2. The crystal structure has been solved from single-crystal data by means of Patterson and Fourier synthesis (R = 0.043, 2218 hkl). The structure, related to the brucite type, is built up from OH- ion layers parallel to (100) with 3 4 of the octahedral holes filled with cadmium atoms. The remaining metal atoms are located above and below the empty octahedral sites; they are sixfold coordinated by three OH-, one water molecule, and one bidentate nitrate group. The thermal decomposition of this compound was investigated by means of TRXD and TG methods. It proceeds in four or three stages, depending upon the environmental atmosphere. Under vacuum, the hemihydrate Cd5(OH)8(NO3)2 · 0.5H2O is obtained during the first stage, whereas a new anhydrous hydroxide nitrate is displayed in the second one. © 1991.