The rare earth metal hydride tellurides REHTe (RE=Y, La–Nd, Gd–Er)

Abstract

The synthesis and crystal structure of a series of rare earth metal hydride tellurides with the composition REHTe (RE = Y, La–Nd, Gd–Er) is reported. These compounds have been obtained by the reaction of rare earth metal dihydrides (REH2) with elemental tellurium in sealed tantalum capsules at T = 700°C using cesium chloride (CsCl) as fluxing agent, which can be washed away with water due to the astonishing insensitivity of these hydride tellurides (REHTe) against hydrolysis. All of the compounds crystallize in the hexagonal space group P6̅m2 with a filled WC-type crystal structure, exhibiting a mutual trigonal-prismatic coordination of the heavy ions (RE3+ and Te2−), while the hydride anions reside in the trigonal prismatic voids surrounded by three rare earth metal cations expanding their coordination pattern to a tricapped trigonal prism. This 1H-type crystal structure is compared with the 1H- and 2H-type structures of the respective hydride selenides (REHSe, RE = Y, La–Nd, Gd–Tm, Lu). Both hexagonal basic crystal structures can be derived from the AlB2-type structure as demonstrated in a Bärnighausen tree by group-subgroup relationships.

Hydrogenation Reaction Pathways and Crystal Structures of La2H2Se, La2H3Se and La2H4Se

“…The phase width of La 2 D 2− x Se underlines the presumably metallic nature of this hydride selenide. The non‐stoichiometry with respect to deuterium (0≤ x ≤0.40) is the only marked difference to a former description of the crystal structure of La 2 D 2− x Se, where deuterium was assumed to show full occupation [9] …”

“…[14] Additional voids with tetrahedral and trigonal-planar coordination remain unoccupied, allowing for the accommodation of further hydrogen atoms. [9] Hydrides with higher hydrogen content are indeed found. For La 2 H 3 Se and La 2 H 4 Se the Ba 2 H 3 Cl [17] and the Ce 2 F 4 Se type [18] were assigned, respectively, on the basis of X-ray diffraction.…”

“…The non-stoichiometry with respect to deuterium (0 � x � 0.40) is the only marked difference to a former description of the crystal structure of La 2 D 2À x Se, where deuterium was assumed to show full occupation. [9] The low phase fraction of La 2 D 3 Se does not allow for a reliable refinement of its occupancy factors. No conclusions concerning a presumed phase width can be drawn from this experiment.…”

“…Thin films of RE O x H 3−2 x phases for RE =Sc, Y, La, Sm−Lu revealed a broad phase width of 0.5≤ x ≤1.5 [8] . Analogous compounds with tellurium with the formula RE HTe crystallize in a stuffed WC type structure ( P m 2) for RE =Y, La−Nd, Gd−Er, Lu [9–11] . The analogous hydride selenides RE HSe adopt two different stuffed structure types: anti ‐NiAs type ( P 6 3 /mmc) for RE =La−Nd or WC type ( P m 2) for RE =Y, Gd−Er, Lu [12,13] .…”

“…[8] Analogous compounds with tellurium with the formula REHTe crystallize in a stuffed WC type structure (P � 6m2) for RE = Y, LaÀ Nd, GdÀ Er, Lu. [9][10][11] The analogous hydride selenides REHSe adopt two different stuffed structure types: anti-NiAs type (P6 3 / mmc) for RE = LaÀ Nd or WC type (P � 6m2) for RE = Y, GdÀ Er, Lu. [12,13] For another composition, RE 2 H 2 Se, the representatives with RE = Sc, Y, LaÀ Nd, GdÀ Lu crystallize in the Ce 2 O 2 S type structure (P3m1).…”