CRYSTAL-STRUCTURES OF THE NEW PSEUDO-ISOTYPIC COMPOUNDS NAFE(SEO3)(2)AND BACO(SEO3)(2)

The new compounds NaFe(SeO3)(2) and BaCo(SeO3)(2) have been synthesize d under low hydrothermal conditions. Their crystal structures have bee n determined using single-crystal X-ray diffraction data and refined t o R(1) = 0.039, 0.020 and wR(2) = 0.075, 0.040 [space group Pnma, Z = 4; NaFe(SeO3)(2); a = 12.553(6), b = 5.349(2), c = 7.899(3) Angstrom, V = 530.4 Angstrom(3); BaCo(SeO3)(2); a = 15.115(2), b = 5.481(1), c = 7.209(2) Angstrom, V = 597.2 Angstrom(3)]. NaFe(SeO3)(2), which is is otypic with KFe(SeO3)(2), is built up by NaO8 polyhedra, FeO6 octahedr a and two types of trigonal SeO3 pyramids to a framework structure. Th e atomic arrangement in BaCo(SeO3)(2) is pseudo-isotypic to NaFe(SeO3) (2), major differences are observed only in the orientation of half of the selenite groups.