Institute of Solid State Physics, Vienna University of Technology, A-1040 Wien, Austria.
Inorg Chem. 2013 Apr 15;52(8):4185-97. doi: 10.1021/ic301548w. Epub 2013 Mar 29.
Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt4B, CeCo4B type, P6/mmm, a = 0.56167(2) nm, c = 0.74399(3) nm; Eu3Pt7B2, Ca3Al7Cu2 type as an ordered variant of PuNi3, R3m, a = 0.55477(2) nm, c = 2.2896(1) nm; and Eu5Pt18B(6-x), a new unique structure type, Fmmm, a = 0.55813(3) nm, b = 0.95476(5) nm, c = 3.51578(2) nm. These compounds belong to the CaCu5 family of structures, revealing a stacking sequence of CaCu5-type slabs with different structural units: CaCu5 and CeCo3B2 type in EuPt4B; CeCo3B2 and Laves MgCu2 type in Eu3Pt7B2; and CaCu5-, CeCo3B2-, and site-exchange ThCr2Si2-type slabs in Eu5Pt18B(6-x). The striking motif in the Eu5Pt18B(6-x) structure is the boron-centered Pt tetrahedron [BPt4], which build chains running along the a axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt4B and Eu3Pt7B2, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt4B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu3Pt7B2 was found to be extraordinarily large, on the order of 0.2 J/mol K(2).
三种新型铕铂硼化物已通过电弧熔炼组成元素并随后退火合成。它们的特征是通过 X 射线粉末和单晶衍射：EuPt4B，CeCo4B 型，P6/mmm，a = 0.56167(2)nm，c = 0.74399(3)nm；Eu3Pt7B2，Ca3Al7Cu2 型作为 PuNi3 的有序变体，R3m，a = 0.55477(2)nm，c = 2.2896(1)nm；Eu5Pt18B(6-x)，一种新的独特结构类型，Fmmm，a = 0.55813(3)nm，b = 0.95476(5)nm，c = 3.51578(2)nm。这些化合物属于 CaCu5 结构家族，揭示了具有不同结构单元的 CaCu5 型片层的堆积顺序：EuPt4B 中的 CaCu5 和 CeCo3B2 型；Eu3Pt7B2 中的 CeCo3B2 和 Laves MgCu2 型；Eu5Pt18B(6-x) 中的 CaCu5、CeCo3B2 和位交换 ThCr2Si2 型片层。Eu5Pt18B(6-x) 结构中引人注目的主题是硼中心的 Pt 四面体 [BPt4]，它形成沿着 a 轴延伸的链，并通过连接重复的 Eu 多面体的融合末端片段在结构排列中起决定性作用。对两种化合物 EuPt4B 和 Eu3Pt7B2 的物理性质进行了研究。发现这两种化合物分别在 36 和 57 K 下有序磁化。通过磁和比热测量证实了 Eu 原子的混合价态。此外，Eu3Pt7B2 的比热的 Sommerfeld 值非常大，约为 0.2 J/mol·K(2)。
