Cs₇Nd₁₁(SeO₃)₁₂Cl₁₆: First Noncentrosymmetric Structure among Alkaline-Metal Lanthanide Selenite Halides

Abstract

Cs7Nd11(SeO3)12Cl16, the complex selenite chloride of cesium and neodymium, was synthesized in the NdOCl-SeO2-CsCl system. The compound has been characterized using single-crystal X-ray diffraction, electron diffraction, transmission electron microscopy, luminescence spectroscopy, and second-harmonic-generation techniques. Cs7Nd11(SeO3)12Cl16 crystallizes in an orthorhombic unit cell with a = 15.911(1) Å, b = 15.951(1) Å, and c = 25.860(1) Å and a noncentrosymmetric space group Pna2(1) (No. 33). The crystal structure of Cs7Nd11(SeO3)12Cl16 can be represented as a stacking of Nd11(SeO3)12 lamellas and CsCl-like layers. Because of the layered nature of the Cs7Nd11(SeO3)12Cl16 structure, it features numerous planar defects originating from occasionally missing the CsCl-like layer and violating the perfect stacking of the Nd11(SeO3)12 lamellas. Cs7Nd11(SeO3)12Cl16 represents the first example of a noncentrosymmetric structure among alkaline-metal lanthanide selenite halides. Cs7Nd11(SeO3)12Cl16 demonstrates luminescence emission in the near-IR region with reduced efficiency due to a high concentration of Nd(3+) ions causing nonradiative cross-relaxation.

Rare‐Earth Cadmium Tellurite Chlorides with a Structural Type Exhibiting [Ln12(TeO3)12] Slabs Alternating with CdCl6 Octahedral Layers

“…These new phases exactly correspond to the targeted sequence of [Ln 12 (TeO 3 ) 12 ] 12+ slabs and are similar to the [Ln 11 (SeO 3 ) 12 ] 9+ slabs described above, with the NaCl‐derived [Cd 6 Cl 24 ] 12– layers being, therefore, the first representatives of a new 2D salt‐inclusion structure type. The structure of III represents a superstructure to that of compounds I and II caused by doubling of the c axis, which is quite common for the related A 7 Ln 11 (SeO 3 ) 2 X 16 compounds (A = alkali metal, X = halogen19–20).…”

“…After annealing, the cadmium halide flux was dissolved at room temperature in distilled water. Initial attempts to grow crystals of the target compounds under conditions employed in the synthesis of selenium compounds18–20 provided only microcrystalline powders. Primary X‐ray checks of the washed samples yielded rather complex patterns wherein most strong lines could be indexed on the basis of tetragonal cells with a ≈ 4 Å and c ≈ 13 Å, which are the expected subcell parameters for the target structures, for Ln = La–Gd.…”

Cs7Sm11[TeO3]12Cl16 and Rb7Nd11[TeO3]12Br16, the new tellurite halides of the tetragonal Rb6LiNd11[SeO3]12Cl16 structure type

“…Nevertheless, they were finally abandoned due to low refined alkali content; for the Cs/Sm couple, the difference in scattering factors is really unfavorable. The same question was raised by Lipp and Schleid [21] in discussion of the structure of Rb 6 LiPr 11 [SeO 3 ] 12 Cl 16 , where the void looks on the contrary too large for Li + . As yet, it is possible to imagine that the alkali cations actually reside mostly in the cubic position, but at least partially in the other positions.…”

“…A large group of compounds therein adopt layered structures [14][15][16][17][18][19][20][21][22][23][24]; those containing Se IV and Te IV exhibit particularly complex architectures briefly reviewed in [14]. A variety of these are layered and contain [M 11+x (ChO 3 ) 12 ] n+ 2D frameworks (M = Ln or Bi, in some cases partially substituted by Mn, Co, Ni, Cu II , Ca, Sr, or Li, x = 0 or 1; Ch = Se or Te, n = 8, 9, or 12).…”

“…Shleid et al [23] 16 and noted that the tellurium compounds of the like were yet very rare. In the current paper, we describe some more representatives and demonstrate that the family may indeed be extended much further.…”