title: Similarities and peculiarities between the crystal structures of the hydrates of sodium sulfate and selenate.
abstract: The crystal structures of the two hydrates Na2SeO4·10H2O and Na2SeO4·7.5H2O are studied for the first time. The structures of Na2SO4·10H2O and Na2SO4·7H2O are reinvestigated as a function of temperature with respect to the degree of disorder of the O atoms of SO4(2-) in the decahydrate and the O atom of water in the heptahydrate. For Na2SO4·10H2O, the unit site occupancy factor (SOF) of O atoms of SO4(2-) was determined at 120 K. After the temperature dependence of the lattice parameters was studied from 120 to 260 K, it was shown that SOF decreased from 1.0 at 120 K to 0.247 at room temperature. The interesting fact that two salts with different chemical compositions and different crystal structures (Na2SO4·7H2O, tetragonal, space group P4(1)2(1)2 and Na2SeO4·7.5H2O, monoclinic, space group C2/c) can act mutually as a crystal nucleus is accounted for by similarities in certain fragments of their crystal structures. This phenomenon is attributed to similarities between particular elements of their structures.
authors: Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
authors: Stoyan
authors: S
authors: Kamburov
authors: Institute of Inorganic Chemistry, Technische Universität Freiberg, Germany.
authors: Horst
authors: H
authors: Schmidt
authors: Institute of Inorganic Chemistry, Technische Universität Freiberg, Germany.
authors: Wolfgang
authors: W
authors: Voigt
authors: Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
authors: Christo
authors: C
authors: Balarew
keywords: heteroepitaxy of hydrates; nucleation; order/disorder; supersaturated solutions