On Sesquiselenides of the Lanthanoids: Single Crystals of C‐type Ce
2Se
3, U‐type Gd
2Se
3, and Z‐type Lu
2Se
3 Single crystals of lanthanoid sesquiselenides (M
2Se
3;
here: M = Ce, Gd, Lu) are accessible through conversion of the elements (lanthanoid and selenium) in molar ratios of 2:3 within seven days at 850 °C from evacuated silica ampoules if equimolar amounts of NaCl serve as a flux. In the case of Ce
2Se
3 (a = 897.74(6) pm) und Gd
2Se
3 (a = 872.56(5) pm) the cubic C‐type (I4¯3d, Z = 5.333) forms as dark red beads, whereas the orthorhombic Z‐type (Fddd, Z = 16) emerges for Lu
2Se
3 (a = 1125.1(1), b = 798.06(8), c = 2387.7(2) pm) as orange‐yellow bricks. Upon oxidation of monochloride hydrides (MClH
x or A
yMClH
x; M = Ce, Gd, Lu; x = 1; A = Li, Na; y = 0.5) with selenium in arc‐welded tantalum ampoules the same main products appear with C‐Ce
2Se
3 and Z‐Lu
2Se
3, even with a surplus of NaCl or LiCl as fluxing agent. In the case of Gd
2Se
3, however, black‐red needles of the orthorhombic U‐type (Pnma, Z = 4; a = 1118.2(1), b = 403.48(4); c = 1097.1(1) pm) are yielded instead of C‐Gd
2Se
3. C‐Ce
2Se
3 crystallizes in a cation‐deficient Th
3P
4‐type structure (Ce
2S
3 type) according to Ce
2.667□
0.333Se
4 (Z = 4) or with Z = 5.333 for the empirical formula Ce
2Se
3. Here, Ce
3+ is coordinated by eight Se
2— anions trigon‐dodecahedrally. In U‐Gd
2Se
3 (U
2S
3 type) two crystallographically independent Gd
3+ cations with coordination numbers of 7 (Gd1) and 7+1 (Gd2), respectively, are present, exhibiting mono‐ or bicapped trigonal prisms as coordination polyhedra. The crystal structure of Z‐Lu
2Se
3 (Sc
2S
3 type) shows two different Lu
3+ cations as well, which now both reside in octahedral coordination of six Se
2— anions each.
相似文献