Sr₂Au₆Al₃ and Eu₂Au₆Al₃ – First Representatives of the Sr₂Au₆Zn₃ Type with Aluminum Triangles

Abstract

The aluminides Sr 2 Au 6 Al 3 and Eu 2 Au 6 Al 3 were synthesized by melting the elements in sealed tantalum tubes in a muffle or induction furnace. The samples were characterized by powder and single-crystal X-ray diffraction: Sr 2 Au 6 Zn 3 type, R3̄c, a = 845.1(1), c = 2177.2(3) pm, wR2=0.0263, 520 F 2 values, 20 variables for Sr 2 Au 6.18(1) Al 2.82(1) , and a = 838.0(1), c = 2177.1(7) pm, wR2 = 0.0276, 510 F 2 values, 19 variables for Eu 2 Au 6 Al 3 . The gold atoms build up diamond-related networks of slightly distorted tetrahedra in the stacking sequence of the 6R polytype (289 - 296 pm Au-Au in Eu 2 Au 6 Al 3 ). The voids left by this network are filled in an ordered manner by strontium (europium) atoms and the rare motif of Al 3 triangles (286 pm Al-Al in Eu 2 Au 6 Al 3 ). The Al 3 triangles in Sr 2 Au 6.18(1) Al 2.82(1) show a small degree of Al/Au mixing.