DTA, DSC and X-ray studies on copper and manganese selenate hydrates

The thermal dehydration of copper and manganese selenate hydrates has been studied by TG, DTA and DSC. The enthalpies of dehydration stages as well as the enthalpies of formation of CuSeO4. 5H(2)O, CuSeO4. H2O, MnSeO4. 5H(2)O, MnSeO4. 2H(2)O and MnSeO4. H2O have been determined. The comparatively lower temperature of CuSeO4. H2O dehydration as compared to the kieserite-type compounds MeSeO4. H2O (Mg, Mn, Co, Ni, Zn) and the formation of CuSeO4. 0.5H(2)O have been discussed in terms of the crystal structures. The dehydration of copper and manganese selenate hydrates has been studied in aqueous and aqueous-acid solutions. A crystallization held of MnSeO4. 4H(2)O is observed in the ternary MnSeO4-H2SeO4-H2O system at 20 degrees C. The strength of the hydrogen bonds in MnSeO4. 2H(2)O and CuSeO4. H2O has been studied by FTIR spectroscopy. Two crystallographically unequivalent water molecules asymmetrically bonded to the metal ions are assumed to exist in MnSeO4. 2H(2)O. The oxygen atoms from water molecules in an almost square planar structure of Cu(H2O)(2)(SeO4)(2) complex form strong hydrogen bonds due to the strong Cu-H2O interaction (synergetic effect). Lattice parameters of CuSeO4. 3H(2)O have been calculated: a = 5.720(2) Angstrom, b = 13.437(4) Angstrom, c = 7.475(2) Angstrom, beta = 97.25(2)degrees, V= 570.0(2) Angstrom(3), SG Cc. (C) 1999 Elsevier Science B.V. All rights reserved.