Design of a new family of inorganic compounds Ae2F2SnX3 (Ae = Sr, Ba; X = S, Se) using rock salt and fluorite 2D building blocks.

We could predict the structure of a new family of compounds Ae(2)F(2)SnX(3) (Ae = Sr, Ba; X = S, Se) from the stacking of known 2D building blocks of the rock salt and fluorite types. With a high-temperature ceramic method we have then succeeded to synthesize the four compounds Ba(2)F(2)SnS(3), Ba(2)F(2)SnSe(3), Sr(2)F(2)SnS(3), and Sr(2)F(2)SnSe(3). The structure refinements from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds results from the alternated stacking of fluorite [Ae(2)F(2)] (Ae = Sr, Ba) and distorted rock salt [SnX(3)] (X = S, Se) 2D building blocks. As shown by band structure calculations, these blocks behave as a charge reservoir and a charge acceptor, respectively. Sr(2)F(2)SnS(3) and Ba(2)F(2)SnS(3) are transparent with optical gaps of 3.06 and 3.21 eV, respectively. However, an attempt to obtain a transparent conductor by substituting Ba per La in Ba(2)F(2)SnS(3) was unsuccessful.

A mixed-valent niobium oxysulfide, La2Nb3S2O8.

Dilanthanum triniobium disulfide octaoxide, La(2)Nb(3)S(2)O(8), crystallizes in the orthorhombic space group Pnnm and is isostructural with the Ln(2)Ta(3)X(2)O(8) (Ln = La, Ce, Pr and Nd, and X = S and Se) family of tantalum compounds. Nb(4+) and Nb(5+) ions co-exist in the structure and occupy different crystallographic sites. While the Nb(4+) ions are found in mixed oxygen and sulfur octahedra, the Nb(5+) ions are found in oxygen-only octahedra.

A new lanthanum titanium oxysulfide, La(16)Ti(5)S(17+x)O(17), with x = 0.75 (9).

The title compound, hexadecalanthanum pentatitanium heptadecasulfide heptadecaoxide, La(16)Ti(5)S(17+x)O(17) [x = 0.75 (9)], has been obtained as a by-product in the preparation of new oxychalcogenide compounds in the La/Ti/Ag/S/O system. La(16)Ti(5)S(17+x)O(17) crystallizes in the tetragonal system (space group I4/m) and is isostructural with Nd(16)Ti(5)S(17)O(17). The structure of the title compound consists of an [La(2)S(2)] rock-salt-type framework, which delimits [001] square channels containing two types of chains of corner-sharing Ti(O,S)(6) octahedra. These chains are connected through La(O,S)(n) polyhedra.