Accidental formation of Gd4(SiO4)2OTe: crystal structure and spectroscopic properties.

Designing new functional materials with increasingly complex compositions is of current interest in science and technology. Complex rare-earth-based chalcogenides have specific thermal, electrical, magnetic and optical properties. Tetragadolinium bis[tetraoxidosilicate(IV)] oxide telluride, Gd4(SiO4)2OTe, was obtained accidentally while studying the Gd2Te3-Cu2Te system. The crystal structure was determined by means of single-crystal X-ray diffraction. The compound crystallizes in the space group Pnma. Three symmetry-independent gadolinium sites were determined. The excitation and emission spectra were collected at room temperature and at 10 K. Gd4(SiO4)2OTe appears to be a promising optical material when doped with rare-earth ions.

Ln3M(1-delta)TX7--quasi-isostructural compounds: stereochemistry and silver-ion motion in the Ln3Ag(1-delta)GeS7 (Ln = La-Nd, Sm, Gd-Er and Y; delta = 0.11-0.50) compounds.

The crystal structures of the Ln3Ag(1-delta)GeS7 (Ln = La-Nd, Sm, Gd-Er, Y; delta = 0.11-0.50, space group P6(3)) compounds were determined by means of X-ray single-crystal diffraction and the similarities among the crystal structures of all Ln3M(1-delta)TX7 (space group P6(3); Ln--lanthanide element, M--monovalent element; T--tetravalent element and X--S, Se) compounds deposited in the Inorganic Crystal Structure Database (ICSD) are discussed. Substitutions of each element in Ln3M(1-delta)TX7 result in a different structural effect. On the basis of the data deposited in the ICSD the large family of the Ln3M(1-delta)TX7 compounds was divided into three groups depending on the position of the monovalent element in the lattice. This position determines what kind of stereoisomer is present in the structure, either the ++ enantiomer or the +- diastereoisomer. Since the silver ions can occupy a different position and the energy barriers between positions are low the ions can move through the channel. It was shown that this movement is not a stochastic process but a correlated one.

Crystal architecture of R(2)SnS(5) (R = Pr, Nd, Gd and Tb): crystal structure relationships in chalcogenides.

The crystal structure of the R(2)SnS(5) (R = Pr, Nd, Gd and Tb) compounds has been investigated using X-ray single-crystal diffraction. Crystal architecture and structural relationships among U(3)S(5), Y(2)HfS(5), R(2)SnS(5) compounds are discussed and a structural origin is determined. It is shown that the complex architecture of the crystal structure of Eu(5)Sn(3)S(12) is a result of interweaving of the simple crystal structures. The location of the copper ions in the non-stoichiometric compound Y(2)Cu(0.20)Sn(0.95)S(5) is proposed on the basis of comparative analysis of the R-S interatomic distances in the R(2)SnS(5) series of compounds.