THE PRASEODYMIUM HYDROGENSELENITE PR2(HSEO3)2(SEO3)2 - SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURE

Crystal growth of praseodymium hydrogenselenite Pr2 (HSeO3)2(SeO3)2 has been carried out by pseudohydrothermal synthesis. Its thermal decomposition gives rise to three new anhydrous rare-earth selenites, two of them isolated as tiny single crystals (Pr2Se4O11 and Pr2SeO9). The structure of Pr2(HSeO3)2(SeO3)2 has been solved in the orthorhombic symmetry, space group Pbc2(1), with unit-cell parameters a = 7.0471(8), b = 8.3480(8), and c = 18.987(3) angstrom, and refined down to R = 0.040 and R(w) = 0.047. Two crystallographically independent types of Pr atoms were found, coordinated to 10 0, giving rise to a tetradecahedron or cis-bicappped cube. The four present Se atoms are coordinated at 3 0 (Se1 and Se4) or at one OH and 2 0 (Se2 and Se3), in the classical form of a trigonal pyramid. Each Se1 and Se4 are linked to five praseodymium atoms, two bidentate and three monodentate bonding, while each Se2 and Se3 only bond one time bidentately and monodentately with Pr2 and Prl, respectively. The structure can be described as a layered one, the sheets containing all the praseodymium and selenite groups are interconnected by hydrogen selenite groups, via hydrogen bonding. This material was also characterized by IR spectroscopy and magnetic measurements. (C) 1994 Academic Press, Inc.