Triangular Zn₃and Ga₃units in Sr₂Au₆Zn₃, Eu₂Au₆Zn₃, Sr₂Au₆Ga₃, and Eu₂Au₆Ga₃– structure, magnetism,¹⁵¹Eu Mössbauer and^69;71Ga solid state NMR spectroscopy

Abstract

Abstract The gold-rich intermetallic compounds Sr 2 Au 6 Zn 3 , Eu 2 Au 6 Zn 3 , Sr 2 Au 6 Ga 3 , and Eu 2 Au 6 Ga 3 were synthesized from the elements in sealed tantalum ampoules in induction or muffle furnaces. The europium compounds are reported for the first time and their structures were refined from single crystal X-ray diffractometer data: Sr 2 Au 6 Zn 3 type, R 3̅ c , a = 837.7(1), c = 2184.5(4) pm, wR 2 = 0.0293, 572 F 2 values for Eu 2 Au 6.04 Zn 2.96 and a = 838.1(2), c = 2191.7(5) pm, wR 2 = 0.0443, 513 F 2 values for Eu 2 Au 6.07 Ga 2.93 with 20 variables per refinement. The structures consist of a three-dimensional gold network with a 6R stacking sequence, similar to the respective diamond polytype. The cavities of the network are filled in a ratio of 2:1 by strontium (europium) atoms and Ga 3 (Zn 3 ) triangles in an ordered manner. Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 are diamagnetic with room temperature susceptibilities of –3.5 × 10 −4 emu mol –1 . Temperature dependent susceptibility and 151 Eu Mössbauer spectroscopic measurements show a stable divalent ground state for both europium compounds. Eu 2 Au 6 Zn 3 and Eu 2 Au 6 Ga 3 order antiferromagnetically below Néel temperatures of 16.3 and 12.1 K, respectively. Anisotropic electrical conductivity of Sr 2 Au 6 Ga 3 is proven by an alignment of the crystallites in the magnetic field. Orientation-dependent 69;71 Ga NMR experiments combined with quantum mechanical calculations (QM) give evidence for a highly anisotropic charge distribution of the Ga atoms.