Anhydrous selenites of lanthanum: Syntheses and crystal structures of La-2(SeO3)(3) and LaFSeO3

Colorless single crystals of La-2(SeO3)(3) were obtained via the decomposit ion of La-2(SeO4)(3) in the presence of NaCl in sealed gold ampoules. The c ompound crystallizes in the orthorhombic system (Pnma, Z = 4, a = 846.7(1). b = 1428.6(1), c = 710.3(2)pm, R-all = 0.0223) and contains La3+ in tenfol d coordination of oxygen atoms which belong to seven SeO32- groups. Hence, three of the latter act as bidentate ligands. The reaction of LiF with La-2 (SeO4)(3) in sealed gold ampoules yielded colorless single crystals of LaFS eO3 (monoclinic, P2(1)/c, Z = 12, a = 1819.8(3), b = 715.75(8), c = 846.4(1 ) pm, beta = 96.89(2)degrees, R-all = 0.0352). The crystal structure contai ns three crystallographically different La3+ ions. La1 is surrounded by six oxygen atoms from five SeO32- groups and four fluoride ions, La2 is coordi nated by two bidentate SeO32- ions and seven fluoride ligands. La3 is surro unded by oxygen atoms only with the coordination number and polyhedron bein g almost the same as found for La3+ in La-2(SeO3)(3). Furthermore, the crys tal structures of both compounds are strongly influenced by the lone pairs of the SeO32- groups.