The formula Ln₅OF₅Se₄ (Ln = Nd and Sm) represents a new composition for lanthanoid(III) oxide fluoride selenides. Nd₅OF₅Se₄ could be seen as aristotype of this system, crystallizing in the tetragonal crystal system with space group I4/mmm and the lattice parameters a = 404.53(2) pm and c = 3400.02(18) pm (c/a = 8.4, Z = 2). In contrast to the aristotype, Sm₅OF₅Se₄ exhibtis a symmetry reduction and adopts space group Ccce with lattice parameters of a = 564.85(3) pm, b = 3391.79(18) pm, c = 564.83(3) (b/c ≈ b/a = 6.0, pm Z = 4). Both compounds can be described by a layered arrangement of sheets, which are formed by the coordination polyhedra surrounding the three crystallographically independent Ln³⁺ cations in eight- and nine-fold coordination of anions. For reasons of electroneutrality one light-anion position has to be mixed-occupied with oxide (O²⁻) and fluoride (F⁻) anions for both compounds. Ln₅OF₅Se₄, with edge-sharing [FLn₄]¹¹⁺ and [(O,F)Ln₄]^10.75+ tetrahedra linked to single and double layers separated by Se²⁻ slabs, shows strong structural analogies to Er₃OF₃S₂. In the case for Sm₅OF₅Se₄ the absence of Sm²⁺ has been well supported by bond-valence calculations and XANES spectroscopy, while recorded DRS measurements were ambiguous owing to the red color of the substance.

分子式Ln ₅ OF ₅ Se ₄（Ln = Nd和Sm）代表一种镧系元素（III）氧化物氟化硒的新组成。Nd ₅ OF ₅ Se ₄可以看作是该系统的贵族型，在空间群为I 4 / mmm且晶格参数为a = 404.53（2）pm和c = 3400.02（18）pm的四方晶体系统中结晶（c / a = 8.4，Z = 2）。与贵族型相反，Sm ₅ OF ₅ Se ₄exhibtis对称还原，并采用空间群CCCE用的晶格参数一个= 564.85（3）时，b = 3391.79（18）时，Ç = 564.83（3）（b / ç ≈B / A = 6.0，PM ž = 4 ）。两种化合物都可以通过薄片的分层排列来描述，这些薄片是由在阴离子的八倍和九倍配位下围绕三个晶体学独立的Ln ³⁺阳离子的配位多面体形成的。电中性的原因之一光阴离子位置必须混合占用与氧化物（O ^2-）和氟化（F ^- ）的阴离子两种化合物。LN ₅作者₅硒₄，用了共享边缘的[F LN ₄ ] ¹¹⁺和[（O，F）LN ₄ ] ^10.75+四面体连接到单，双分离各层由硒^2-板坯，示出了强结构类比来尔₃的₃ S ₂。对于Sm ₅ OF ₅ Se ₄，键合价计算和XANES光谱法很好地支持了Sm ²⁺的缺失，而记录的DRS测量结果由于该物质的红色而模棱两可。