Bie Haiying, Mar Arthur
Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada.
Chem Asian J. 2009 Sep 1;4(9):1465-73. doi: 10.1002/asia.200900063.
The ternary rare-earth germanium antimonides RE(12)Ge(7-x)Sb(21) (RE = La-Pr; x = 0.4-0.5) are synthesized by direct reactions of the elements. Single-crystal X-ray diffraction studies indicate that they adopt a new structure type (space group Immm, Z = 2, a = 4.3165(4)-4.2578(2) A, b = 15.2050(12)-14.9777(7) A, c = 34.443(3)-33.9376(16) A in the progression from RE = La to Pr), integrating complex features found in RE(6)Ge(5-x)Sb(11+x) and RE(12)Ga(4)Sb(23). A three-dimensional polyanionic framework, consisting of Ge pairs and Sb ribbons, outlines large channels occupied by columns of face-sharing RE(6) trigonal prisms. These trigonal prisms are centered by additional Ge and Sb atoms to form GeSb(3) trigonal-planar units. A bonding analysis attempted through a Zintl-Klemm approach suggests that full electron transfer from the RE atoms to the anionic substructure cannot be assumed. This is confirmed by band-structure calculations, which also reveal the importance of Ge-Sb and Sb-Sb bonding. Magnetic measurements on Ce(12)Ge(6.5)Sb(21) indicate antiferromagnetic coupling but no long-range ordering down to 2 K.
三元稀土锗锑化物RE(12)Ge(7 - x)Sb(21)（RE = La - Pr；x = 0.4 - 0.5）通过元素的直接反应合成。单晶X射线衍射研究表明它们采用了一种新的结构类型（空间群Immm，Z = 2，从RE = La到Pr的过程中，a = 4.3165(4) - 4.2578(2) Å，b = 15.2050(12) - 14.9777(7) Å，c = 34.443(3) - 33.9376(16) Å），整合了在RE(6)Ge(5 - x)Sb(11 + x)和RE(12)Ga(4)Sb(23)中发现的复杂特征。一个由Ge对和Sb带组成的三维聚阴离子框架勾勒出由共面的RE(6)三角棱柱列占据的大通道。这些三角棱柱由额外的Ge和Sb原子居中，形成GeSb(3)三角平面单元。通过Zintl - Klemm方法进行的键合分析表明，不能假定RE原子向阴离子亚结构有完全的电子转移。能带结构计算证实了这一点，该计算还揭示了Ge - Sb和Sb - Sb键合的重要性。对Ce(12)Ge(6.5)Sb(21)的磁性测量表明存在反铁磁耦合，但在2 K以下没有长程有序。
