C-type Nd₂Se₃

Abstract

The title compound, neodymium sesquiselenide, is isotypic with the other known rare-earth metal(III) selenides M 2Se3 (M = La–Pr and Sm–Lu) with the cubic C-type structure. It adopts a cation-defective Th3P4-type arrangement with close to 8/9 of the unique neodymium-cation site occupied, leading to the composition Nd2.667Se4 (Z = 4) or Nd2Se3 (Z = 5.333), respectively. The Nd3+ cations are thus surrounded by eight selenide anions, forming trigonal [NdSe8]13− dodeca­hedra, whereas the Se2− anions exhibit a sixfold coordination, but due to the under-occupation of neodymium, each one is statistically surrounded by only 5.333 cations. The crystal studied was a merohedral twin with a 0.31 (6):0.69 (6) domain ratio.

Syntheses and Crystal Structures of CsCuNd2Se4 and CsCuGd2Te4: Two Non‐Isotypical Cesium Copper Lanthanide Chalcogenides with {}^1_\infty{[CuCh3]5–} Chains of Vertex‐Shared [CuCh4]7– Tetrahedra

“…The [ LnCh 6 ] 9– octahedra are also distorted, comprising Se–Nd–Se angles in intervals of 82 to 96° and 165 to 177° for CsCuNd 2 Se 4 or Te–Gd–Te angles with values of 89–96° and 171–179° in CsCuGd 2 Te 4 . The distances d (Nd–Se) that range between 289 and 304 pm in CsCuNd 2 Se 4 , are in fair agreement with those of Nd 2 Se 3 ( d (Nd–Se) = 297–317 pm, CN(Nd 3+ ) = 8) 20 and CuNdSe 2 ( d (Nd–Se) = 293–316 pm, CN(Nd 3+ ) = 6) 21. The distances between Gd 3+ and Te 2– in CsCuGd 2 Te 4 covering an interval from 300 to 318 pm are consistent for example with those in Gd 2 Te 3 ( d (Gd–Te) = 311–367 pm, CN(Gd 3+ ) = 7 and 8) 22 and in Cs 3 Cu 5 Gd 4 Te 10 ( d (Gd–Te) = 297–327 pm, CN(Gd 3+ ) = 6) 11.…”

Structure Evolutions and Metallic Transitions in In2Se3 Under High Pressure

“…The Se–In–Se–In–Se quintuple layer is the infinite two-dimensional structure paralleled the ab -plane, in which the atoms stack five layers along the c -axis. For the larger Ln cations (Ln = Gd, Sm, Nd, Pr, Ce, La), Ln 2 Se 3 adopts the isostructural cubic lattice with phase IV of In 2 Se 3 . − Therefore, the transformation from phase III′ to IV in In 2 Se 3 under compression is similar to the evolution of Ln 2 Se 3 at ambient pressure with the increasing Ln cations radius, but without the intermediate primitive orthorhombic structure (Ln = Dy, Tb, Gd, Sm; space group Pnma ). ,,, …”

“…And then, phase IV remains a stable structure up to the maximum experimental pressure of 59.5 GPa. Phase IV of In 2 Se 3 adopts a defective Th 3 P 4 -type structure, which is isostructural with Ln 2 Se 3 (Ln = Gd, Sm, Nd, Pr, Ce, La). − The schematic view of crystal structure of phase IV is shown in Figure , as well as the InSe 8 dodecahedron and SeIn 6 octahedron. In and Se ions occupy the 12a and 16c positions, respectively, with the site occupation factor (sof) in the In position of 8/9 in order to satisfy the ratio of 2:3 for In:Se in In 2 Se 3 .…”

About Lanthanoid Fluoride Selenide Oxoselenotantalates with the Composition Ln3F2Se2TaO4 (Ln = La – Nd)

“…The Madelung Part of the Lattice Energy (MAPLE according to Hoppe) [48][49][50] shows a lower value for all Ln 3 F 2 Se 2 TaO 4 representatives with Ln = La -Nd than the sum of the formally underlying binaries or ternaries (i.e. LnTaO 4 (P2 1 /c), [3,27] Ln 2 Se 3 (I43d), [51][52][53] and LnF 3 (P3c1) [54][55][56][57] ) by 4.5 to 6.0 %. The MAPLE sum for this comparison was calculated according to 1 / 3 (3 ϫ MAPLE(LnTaO 4 ) + 2ϫ MAPLE(Ln 2 Se 3 ) + 2 ϫ MAPLE(LnF 3 )) and the respective values can be seen in Table 6.…”