Triangular Zn3 and Ga3 units in Sr2Au6Zn3, Eu2Au6Zn3, Sr2Au6Ga3, and Eu2Au6Ga3 – structure, magnetism, 151Eu Mössbauer and 69;71Ga solid state NMR spectroscopy

Abstract

Abstract The gold-rich intermetallic compounds Sr2Au6Zn3, Eu2Au6Zn3, Sr2Au6Ga3, and Eu2Au6Ga3 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: Sr2Au6Zn3 type, R3̅c, a = 837.7(1), c = 2184.5(4) pm, wR2 = 0.0293, 572 F 2 values for Eu2Au6.04Zn2.96 and a = 838.1(2), c = 2191.7(5) pm, wR2 = 0.0443, 513 F 2 values for Eu2Au6.07Ga2.93 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 Ga3 (Zn3) triangles in an ordered manner. Sr2Au6Zn3 and Sr2Au6Ga3 are diamagnetic with room temperature susceptibilities of –3.5 × 10−4 emu mol–1. Temperature dependent susceptibility and 151Eu Mössbauer spectroscopic measurements show a stable divalent ground state for both europium compounds. Eu2Au6Zn3 and Eu2Au6Ga3 order antiferromagnetically below Néel temperatures of 16.3 and 12.1 K, respectively. Anisotropic electrical conductivity of Sr2Au6Ga3 is proven by an alignment of the crystallites in the magnetic field. Orientation-dependent 69;71Ga NMR experiments combined with quantum mechanical calculations (QM) give evidence for a highly anisotropic charge distribution of the Ga atoms.