ABSTRACT
A new oxyfluorotellurate(IV), indium fluoridopentaoxidotellurate(IV), InTe2O5F, has been synthesized by solid-state reaction and structurally characterized. The crystal structure consists of a three-dimensional framework formed by InO4F2 octahedra and Te2O5 units. The InO4F2 octahedra are linked through the F atoms, which lie on twofold axes, giving rise to helical chains. These helical chains are connected via the Te2O5 units. The helical chains of indium octahedra surround cavities, into which the lone pairs of electrons of the Te atoms point.
ABSTRACT
The structure of an already evidenced but still uncharacterized GeTe(2)O(6) phase consists of isolated GeO(6) octahedra connected via isolated TeO(3) units. The germanium cations occupy a site with 1 symmetry. The Te and O atoms are in general positions of the P2(1)/n space group. This structure corresponds to a new type of tetravalent tellurate and is different from other AB(2)X(6) structures in which the B cation presents a stereochemically active electronic lone pair. It derives from the pseudo-hexagonal MI(2)O(6) (M = Mg, Mn, Co and Fe) type by a strong monoclinic distortion caused by the much smaller size of Ge(4+) compared with the divalent M cations.
ABSTRACT
As an extension of a general structural study concerning fluorides and oxyfluorides of cations presenting a stereochemically active electronic lone pair, until now limited to tellurium(IV) phases, the previously unknown structure of NaIO(2)F(2) corresponds to a new structure type based on isolated IO(2)F(2)(-) polyhedra forming sheets separated by Na(+) layers. The sodium ion is octahedrally coordinated with 2/m site symmetry, while the I(V) atom has m2m symmetry with a stereochemically active lone electron pair. The O and F atoms (both with m symmetry) are bonded to the I(V) atoms in a fully ordered manner. A comparison with the structure of ferroelastic KIO(2)F(2) and with structures based on hexagonal close packing of anions, mainly rutile-type and FeTeO(3)F-type, reveals differences that are attributed to the smaller ionic radius of Na(+) and the ordering of the Na and I cations.
ABSTRACT
In the course of a general study of oxyfluorotellurates(IV), materials likely to exhibit interesting nonlinear optical properties, the crystal structures of the new phases scandium tellurium trioxide fluoride, ScTeO(3)F, and indium tellurium trioxide fluoride, InTeO(3)F, belonging to two different structural types and also differing from that of the recently published MTeO(3)F (M = Fe, Ga and Cr) series, have been determined. The ScTeO(3)F structure can be described as an intergrowth of two different layers of scandium octahedra connected via isolated TeO(3) groups. The scandium ions occupy two different sites with ..2 and 2.. site symmetry. The Te, F and O atoms are on general positions of the Pnna space group. The InTeO(3)F structure consists of zigzag sheets of InO(5)F octahedra. The In, Te, O and F atoms are all located on general positions of the P2(1)/a space group. TeO(3)F polyhedra are inserted between the zigzag sheets of InO(5)F octahedra and with them form double (InTeO(3)F)(n) layers. Therefore, InTeO(3)F is a true layer structure, unlike the previous types. In all these phases, the electronic lone pair of the Te(IV) atom is stereochemically active and a full O/F anionic ordering is observed.
ABSTRACT
The crystal structures of the new isomorphous compounds iron(III) oxyfluorotellurate(IV), FeTeO(3)F, gallium(III) oxyfluorotellurate(IV), GaTeO(3)F, and chromium(III) oxyfluorotellurate(IV), CrTeO(3)F, consist of zigzag chains of MO(4)F(2) distorted octahedra alternately sharing O-O and F-F edges and connected via TeO(3) trigonal pyramids. A full O/F anionic ordering is observed and the electronic lone pair of the Te(IV) cation is stereochemically active.
