Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides
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, R3̅m, a = 0.55477(2) nm, c = 2.2896(1) nm; and Eu5Pt18B6–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 Eu5Pt18B6–x. The striking motif in the Eu5Pt18B6–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 K2.
Darstellung und kristallstrukturen der Zink-Iridiumboride ZnIr4B3, Zn6Ir11B6−x, ZnIr2B2 und Zn2Ir2B☆
Abstract Four zinc-iridium borides were prepared by reaction of the elements at 1100 °C in boron nitride crucibles sealed in tantalum ampoules. Their structures were determined by means of single-crystal X-ray methods. ZnIr 2 B 2 (tetragonal, I 4/ mmm ; a =296.31(1) pm; c =1262.08(8) pm; Z =2; 115 reflections; 8 variable parameters; R =0.026) crystallizes with the inverse ThCr 2 Si 2 structure. Layers of edge-connected Ir 4 B tetrahedra are separated by 4 4 networks of zinc atoms. ZnIr 4 B 3 (orthorhombic, Pmmm ; a =279.98(2) pm; b =2317.7(1) pm; c =281.96(2) pm; Z =2; 475 reflections; 23 parameters; R =0.051), Zn 6 IrB 6− x with x =0.6 (orthorhombic, Pmmm ; a =286.80(4) pm; b =847.1(1) pm; c =1138.4(3) pm; Z =1; 1234 reflections; 41 parameters; R =0.038) and Zn 2 Ir 2 B (orthorhombic, Cmcm ; a =280.85(3) pm; b =2657.1(3) pm; c =1023.9(2) pm; Z =12; 689 reflections; 47 parameters; R =0.060) form new structures. All the boron atoms are within trigonal prisms formed by iridium atoms and there are no B-B or B-Zn contacts. The zinc atoms are arranged in layers in ZnIr 4 B 3 , in both layers and chains in Zn 6 Ir 11 B 6− x , and in a three-dimensional framework in Zn 2 Ir 2 B. The electrical conductivities measured between 290 and 4.2 K (pressed and sintered rods, 4-probe d.c. method) show that all compounds are metallic conductors.
Mg2Ru5B4 und Mg5Ru13B11, zwei ternäre Magnesium‐Rutheniumboride mit Kanalstrukturen
Die orthorhombisch in der Raumgruppe Pbam kristallisierenden ternaren Boride Mg2Ru5B4 und Mg5Ru13B11 wurden durch direkte Umsetzung der Elemente in verschweisten Tantalampullen dargestellt. Mg2Ru5B4 (a = 1000,0(2) pm, b = 837,6(1) pm, c = 295,42(3) pm, Z = 2, RW = 0,027 fur 563 Reflexe) ist homootyp mit Sc2Ru5B4. Die Struktur enthalt trigonale BRu6-Prismen, die durch Flachen- und Kantenverknupfung Kanale mit funfeckigem Querschnitt bilden, in denen sich Ketten von Magnesiumatomen befinden. Mg5Ru13B11 (a = 2190,1(2) pm, b = 996,7(2) pm, c = 294,65(3) pm, Z = 2, RW = 0,031 fur 959 Reflexe) hat eine ahnliche, bisher unbekannte Struktur, in der ein Teil der Magnesium- und Boratome fehlgeordnet ist. 
 
 
 
Mg2Ru5B4 and Mg5Ru13B11, Two Ternary Magnesium Ruthenium Borides with Channel Structures 
 
 
 
The ternary borides Mg2Ru5B4 and Mg5Ru13B11, crystallizing in the orthorhombic space group Pbam, were prepared by reaction of the elementary components in sealed tantalum ampoules. Mg2Ru5B4 (a = 1000.0(2) pm, b = 837,6(1) pm, c = 295.42(3) pm, Z = 2, RW = 0.027 for 563 reflections) is homeotypic with Sc2Ru5B4. The structure contains BRu6-trigonal prisms, connected by faces and edges to form pentagonal channels filled with chains of magnesium atoms. Mg5Ru13B11 (a = 2190.1(2) pm, b = 996.7(2) pm, c = 294.65(3) pm, Z = 2, RW = 0.031 for 959 reflections) has a similar but so far unknown structure in which parts of the magnesium and boron atoms are disordered.