Two new binary lanthanide polytellurides: Syntheses and crystal structures of CeTe1.90 and SmTe1.80

Single crystals of the new binaries CeTe1.90 and SmTe1.80 have been obtained. CeTe1.90 was synthesized at 1023 K from the reaction of Ce, TeO2, and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P42/n with 20 formula units in a cell of dimensions at 153 K of image, image, image. It is isostructural with the LnSe1.9 polyselenides (Ln=La, Ce, Pr) and with SmS1.90. SmTe1.80 was synthesized at 1223 K from the reaction of Sm and Te in a KBr flux. SmTe1.80 crystallizes in a new structural type in the tetragonal space group P4/n with 20 formula units in a cell of dimensions at 153 K of image, image, image. Both of these layered structures, which may be derived from the ZrSiS structure type, consist of double layers of [LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te–Te distances are 2.9194(5), 3.1204(5), and 3.3324(6) Å in CeTe1.90 and 2.878(1), 2.9932(3), and 3.2114(7) Å in SmTe1.80. Neither a simple delineation of the Te–Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one takes strict account of the Te–Te distances.