Dehydration steps of aquacopper(II) complexes with homogeneous and heterogeneous coordination sphere are investigated from
the view point of structural changes taking place under their heating to the decomposition temperature and during the dehydration.
The role of loosening of intra-and intermolecular hydrogen bonds in the decomposition reaction for the structure changes of
the remainder, the structural presumptions of the reactants for lower hydrates formation are discussed.
Activation parameters of dehydration were found to be the lower, the smaller are the structure differences between the reactants
and products. They do not reflect the bond length central atomvolatile ligand, much more the overall structure differences
between the starting and resulting compounds. From all data on crystal and molecular structures of dehydrated compounds is
the reaction pathway best indicated by anisotropic temperature parameters of donor atoms corrected for the thermal movement
of the central atom: the higher these values in the bond direction are, the lower the values of activation energies of dehydration
The thermal dehydration of pentacoordinate complexes [Cu(maleinate)(H2O)] (I), [Cu2(citrate) (H2O)2] (II) and [Cu(phenoxyacetate)2(H2O3] (III) was investigated and correlated with the structural changes occurring during the dehydration. It was found that the
activation parameters of the reactions do not follow the lengths of the split Cu−OH2 bonds. The lowestEa and lgA values were found for compound I, the highest ones for compound III. The most expressive changes of the anionic ligand binding
mode take place during the dehydration of this compound.
The study of the thermal dehydration of the compounds CuX2.nH2O, where X− were formate, salicylate or phtalate anions, was performed, including the observations of structural changes of compounds during their decomposition. It is shown that the dehydration of copper(II) formate tetra- and dihydrates is accompanied by significant changes in the bonding of the formato groups and remaining water molecules. Two structurally different modifications of Cu(HCOO)2.2H2O were prepared, the structure differences are clearly demonstrated in their decomposition stoichiometry. The dehydration of copper formate hydrates was found to be controlled by chemical reaction on the phase boundary. The dehydration of the copper salicylate tetrahydrate and copper phtalate monohydrate is accompanied by the structural changes of the whole compounds, as well, however these processes are diffusion or nucleation controlled.
The structures of compounds M2IMII(SEO4)2 (MI=K, Tl; MII=Cu and Ni), were studied using IR, electronic and EPR spectra. The results indicate a hexacoordination of both central atoms, and a bridging function of selenato groups, the mode of their coordination varies with MI and MII. The compound Tl2Cu(SeO4)2 was prepared also in the amorphous glassy form, although with partial decomposition. It is presumed that in the homogeneous smaragd-green material -Cu-O-Cu-, -Cu-OSeO2-Cu- and -Cu-OSeO3-Cu- bridges are present simultaneously. The course of the thermal decomposition of the studied compounds depends on the nature of the MI and MII cations. According to powder X-ray patterns, the decomposition products do not contain individual oxides. Nearly complete removal of selenium was observed in the decomposition of hydrated ammonium double selenates of Ni(II) and Cu(II).
Authors:H. Langfelderovà, M. Linkešová, and E. Jóna
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 · 5 H2O, CuSO4 · 3 H2O and CuSO4 · H2O. The values ofE* andΔS* for the dehydration of CuSO4 · 3 H2O were found to be only little affected by the mode of preparation of this compound. On the other hand, the values ofE* andΔS* for the dehydration of CuSO4 · ·H2O are strongly dependent on whether this compound was prepared by thermal decomposition of CuSO4 · 5 H2O or CuSO4 · 3 H2O, or by crystallization from solution. As regards the crystalline hydrates of copper(II) sulphate, the greatest energetic hindrance for dehydration was observed for CuSO4 · 3 H2O. 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 paper presents the results of a study of M2IMII(SO4)2 compounds withMI= K, Rb, Cs or Tl, andMII=Cu or Ni, in the interval from room temperature to the melting temperature. All the compounds studied show endo- or exothermic excursions in their DTA curves, corresponding to phase transitions connected with colour changes of the compounds. For M2ICu(SO4)2, whereMI is K or Tl, several modifications could be prepared at laboratory temperature, probably distortion isomers. No modifications of this type could be prepared, however, for M2INi(SO4)2 compounds.