No abstract

The paper reports an attempt to correlate the structures of hydrates of copper(II) sulphate with some characteristic features of the kinetics of their thermal decompositions. Non-isothermal thermogravimetric measurements were employed to obtain values of experimental activation energy and entropy for the dehydration of CuSO4 9 5 H~O, CuSO 4 9 3 H20 and CuSO~ 9 H20. The values orE* and AS* for the dehydration of CuSO~ 9 3 H20 were found to be only little affected by the mode of preparation of this compound. On the other hand, the values orE* and AS* for the dehydration of CuSO4 9 9 H20 are strongly dependent on whether this compound was prepared by thermal decomposition of CuSO~ 9 5 H20 or CuSO~ 9 3 H~O, or by crystallization from solution. As regards the crystalline hydrates of copper(lI) sulphate, the greatest energetic hindrance for dehydration was observed for CuSO~ -3 H20. The experimental results are also discussed with respect to the present opinions concerning the possibilities of using thermal analyses to obtain information on the relationship between the structures and reactivities of solids.

The thermal dehydration of the compounds M~[MII(H20)6](SeO4)2, where M 1 = NH4, K, Rb, Cs and T1, and M II = Cu and Ni, was studied in order to correlate the course of the decomposition with the known crystal structures. It was found that the stoiehiometry of the reactions is the same as that established for the analogous sulphato compounds of Cu(II) and Ni(II), respectively. Because of the discrepancies between the room-temperature crystal structures and the observed decomposition stoiehiometries, high-temperature powder diffractograms were taken. These indicated structural changes of the copper(II) compounds during heating. The powder patterns for different structure changes were calculated and compared with the experimental ones. It was shown that during the heating two axial Cu-HzO bonds are shortened and two equatorial bonds are lengthened. The observed decomposition stoichiometry is compatible with the formation of four nearly equal Cu-H20 bonds. The activation energies (E*) and pre-exponential factors (log A) for the first dehydration reaction of the Cu(II) compounds display the following sequence of MI: TI > Rb > NH4 > K, and they are the higher, the shorter the split equatorial Cu(II) bonds. For the compounds of Ni(II) the sequence of E* and log A values is K > TI > NH4 > Rb > Cs. It was shown previously [1, 2] that the symmetry of the Cu(II) coordination polyhedron is one of the important factors influencing the stoichiometryand the kinetics of the thermal decomposition of coordination compounds with Cu(II) as central atom. The fact that compounds with rhombically deformed coordination polyhedra, such as M~[Cu(H20)6](SO4)2, exhibit decomposition stoichiometry which would correspond better to tetragonal John Wiley & Sons, Limited, Chichester Akaddmiai lO'ad6, Budapest