Abstract
The first ternary lanthanide telluride-bromide La3Te4Br was obtained from a mixture of LaTe and LaBr3 (in the presence of iridium) in a sealed tantalum container at elevated temperatures. The crystal structure (orthorhombic, Pnma, a = 1634.3(2), b = 435.0(1), c = 1426.6(2) pm, Z = 4, R1 (I0 > 2s(I0)) = 0.0349) is built from dicapped trigonal prisms of tellurium and bromine atoms surrounding lanthanum in two different ways. The dicapped trigonal prisms are connected via common edges to a threedimensional structure, in the same fashion as is known for the binary U3Te5. La3Te4Br is a valence compound according to (La3+)3(Te2-)4(Br-) and one out of three lanthanide telluride-halides known to date.
Highlights
There is a remarkable difference in our knowledge of chalcogenide-halides RChX of the rare-earth elements (R) when the chalcogen (Ch) part is considered alone; while the oxide-halides ROX, the most prolific compound type, are all known and were structurally characterized at least by powder X-ray diffraction, in many cases by single crystal X-ray structure determination, see for example ref. [1], Crystals 2011, 1 telluride-halides are almost unknown
La1 and La2 are surrounded by seven tellurium atoms with one tellurium and one bromine atom as the caps of two rectangular faces, and La3 is surrounded by six tellurium and two bromine atoms with the bromine atoms forming one edge of the trigonal prism
The three prisms are connected via two common edges (Te2―Te4 and Te3―Br) to a trimeric building unit of the composition La3Te14Br4
Summary
There is a remarkable difference in our knowledge of chalcogenide-halides RChX of the rare-earth elements (R) when the chalcogen (Ch) part is considered alone; while the oxide-halides ROX, the most prolific compound type, are all known and were structurally characterized at least by powder X-ray diffraction, in many cases by single crystal X-ray structure determination, see for example ref. [1], Crystals 2011, 1 telluride-halides are almost unknown. The first, a three-dimensional nonstoichiometric compound, may be derived from the NaCl-type of structure with polytelluride fragments, with tellurium in the oxidation states -2 and -1. The latter, La2TeI2, would be counted as a metal-rich layer compound with condensed octahedral clusters; it has the same structure as 3R-Lu2CCl2 [4], better represented as {CLu2}Cl2 = {TeLa2}I2 [5]. Sc14Os3Te8, or better {Os3Sc12}Te8Sc2-x, has remarkable structural similarities with {Os3Sc12}Br16Sc [22] Both compounds contain the same extended cluster chain of square antiprisms and cubes of scandium atoms (in a 2:1 ratio) with endohedral eight-coordinate osmium atoms! We have not yet accomplished our goal, we have, in the Ir/La/Te/Br system, obtained the first lanthanide telluride bromide, La3Te4Br
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