ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

The Hydrates of Double Selenates

M. Ebert and P. Vojtíšek

Department of Inorganic Chemistry, Faculty of Natural Sciences, Charles University, CZ-128

Abstract: This study deals with the hydrates of double selenates of the type M₂^IM^II(SeO₄)₂ . xH₂O (x = 2 or 6) from the point of view of the effect of the M^I(M^I= K, Rb, Cs, Tl, NH4) and M^II M^II = Mg, Zn, Cd, Mn, Co, Ni, Cu) cations on the water molecules in-the coordination sphere of the bivalent metal. The bonds of the water molecules were studied on the basis of the bands of the ''wagging'' libration modes of the water molecules, and the bands of the stretching vibrations in the infrared molecular spectrum, and using thermal analysis. According to the study of ''wagging'' libration modes the deformation of the coordination sphere of the hexaaqua cations [M^II(H₂O)₆]²⁺ increases with the decreasing radius of cation M⁺ and with the increasing radius of cation M²⁺, and thus the tendency to form dihydrates of the studied double selenates also increases. This dependence corresponds with the thermal decomposition of the hexahydrates to dihydrates. Thermal decomposition of dihydrates to the anhydrous salts is determined primarily by the strength of the hydrogen bonds between the test anions and the water molecules, once again affected by the two types of cations. The NH₄⁺, Tl⁺, Cu²⁺, and Ni²⁺ cations specifically affect the thermal decomposition of the hydrates of the double selenates.

Full paper in Portable Document Format: 475a292.pdf

Chemical Papers 47 (5) 292–296 (1993)