Deng Bin, Ellis Donald E, Ibers James A
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA.
Inorg Chem. 2002 Nov 4;41(22):5716-20. doi: 10.1021/ic020324j.
The compounds RbLnSe(2) (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Ho, Er, Lu) have been synthesized by means of the reactive flux method at 1173 K. These isostructural compounds, which have the alpha-NaFeO(2) structure type, crystallize with three formula units in space group D(3d)(5)-R(-)3m of the trigonal system in cells at T = 153 K of dimensions (a, c in A) La, 4.4313(4), 23.710(3); Ce, 4.3873(3), 23.656(3); Pr, 4.3524(11), 23.655(7); Nd, 4.3231(5), 23.670(4); Sm, 4.2799(4), 23.647(3); Gd, 4.2473(7), 23.689(5); Tb, 4.2197(4), 23.631(3); Ho, 4.1869(6), 23.652(5); Er, 4.1541(8), 23.576(7); Lu, 4.1294(6), 23.614(5). The structure consists of close-packed Se layers in a pseudocubic structure distorted along [111]. The Rb and Ln atoms occupy distorted octahedral sites in alternating layers. The Rb-centered octahedra share edges with the Ln-centered octahedra between layers. Within a given layer, both the Rb-centered and Ln-centered octahedra share edges with themselves. RbTbSe(2) and RbErSe(2) exhibit Curie-Weiss paramagnetism between 5 and 300 K, and RbCeSe(2) exhibits Curie-Weiss paramagnetism between 100 and 300 K. The optical transitions for RbCeSe(2), RbTbSe(2), and RbErSe(2) are in the 2.0-2.2 eV region of the spectrum, both from diffuse reflectance spectra and from first-principles calculations. These calculations also provide insight into the electronic structures and chemical bonding in RbLnSe(2). A quadratic fit for the lanthanide contraction of the Ln-Se distance is superior to the linear one only if the closed-shell atoms La and Lu are included.
化合物RbLnSe₂（Ln = La、Ce、Pr、Nd、Sm、Gd、Tb、Ho、Er、Lu）已通过反应助熔剂法在1173 K下合成。这些等结构化合物具有α-NaFeO₂结构类型，在T = 153 K时，以三个化学式单元结晶于三方晶系的空间群D₃d⁵-R-3m中，晶胞尺寸（a、c，单位为埃）分别为：La，4.4313(4)，23.710(3)；Ce，4.3873(3)，23.656(3)；Pr，4.3524(11)，23.655(7)；Nd，4.3231(5)，23.670(4)；Sm，4.2799(4)，23.647(3)；Gd，4.2473(7)，23.689(5)；Tb，4.2197(4)，23.631(3)；Ho，4.1869(6)，23.652(5)；Er，4.1541(8)，23.576(7)；Lu，4.1294(6)，23.614(5)。该结构由沿[111]方向扭曲的伪立方结构中的紧密堆积Se层组成。Rb和Ln原子占据交替层中的扭曲八面体位置。以Rb为中心的八面体与层间以Ln为中心的八面体共享棱边。在给定层内，以Rb为中心和以Ln为中心的八面体自身都共享棱边。RbTbSe₂和RbErSe₂在5至300 K之间表现出居里-外斯顺磁性，RbCeSe₂在100至300 K之间表现出居里-外斯顺磁性。RbCeSe₂、RbTbSe₂和RbErSe₂的光学跃迁均在光谱的2.0 - 2.2 eV区域，这是通过漫反射光谱和第一性原理计算得出的。这些计算还深入了解了RbLnSe₂的电子结构和化学键。只有当包含闭壳层原子La和Lu时，对Ln - Se距离的镧系收缩进行二次拟合才优于线性拟合。
