SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURE OF ND(HSEO3)(SEO3)CENTER-DOT-2H2O

Single crystals of rare-earth hydrated hydrogenselenite Nd(HSeO3)(SeO3) · 2H2O have been obtained by pseudohydrothermal synthesis, using a glass of composition 10SeO2 : Nd2O3 as precursor. Material characterization was supported by chemical analysis, infrared absorption spectroscopy, and thermal analysis. The latter technique shows the presence of a new rare-earth selenite, Nd2Se4O11, as a subproduct of the thermal decomposition. The Nd(HSeO3)(SeO3) · 2H2O compound crystallizes in the orthorhomobic system, space group P 212121, with unit cell parameters a = 6.699(4) Å, b = 7.101(1) Å and c = 16.39(2) Å. The structure has been determined by X-ray single crystal techniques and refined down to R = 0.043. It can be described as infinite chains of bicapped trigonal prisms (NdO7(H2O)) sharing edges interconnected by (SeO3E) tetrahedra (E lone pair) via corner and edge sharing making a layer (NdSeO6) upon which (SeO2OHE) groups are grafted, assuming the stability of the network via hydrogen bonding. Free water molecules occupy channels developed along [100]. Particular similarities between the layers (NdSeO6) of this structure and the slabs along [010] of the ZrSiO4 structure are emphasized. The coordination number (CN = 8) of Zr and Nd, bisdisphenoid and bicapped trigonal prisms respectively, can be related by a simple topological distorsion. The (SeO3E) tetrahedra play a connecting role analogous to that of SiO4 tetrahedra in the formation of (NdSeO6) layers. © 1994 Academic Press, Inc.