Gold in the Layered Structures of R3Au7Sn3: From Relativity to Versatility

Abstract

A series of isotypes of ternary rare earth element-gold-tetrel intermetallic compounds have been synthesized, and their structures and properties have been characterized. R3Au7Sn3 (R = Y, La-Nd, Sm, Gd-Tm, Lu) crystallize with the hexagonal Gd3Au7Sn3 prototype (Pearson symbol hP26; P63/m, a = 8.110–8.372 Å, c = 9.351–9.609 Å, Vcell = 532.7–583.3 Å3, Z = 2), an ordered variant of the Cu10Sn3-type. Their structures are built up by GdPt2Sn-type layers, which feature edge-sharing Sn@Au6 trigonal antiprisms connected by trigonal R3 groups. Additional insertion of gold atoms leads to the formation of new homoatomic Au clusters, Au@Au6; alternatively, the structure can be considered as a superstructural polyhedral packing of the ZrBeSi-type. The magnetization, heat capacity, and electrical resistivity have been measured for R3Au7Sn3 (R = Ce, Pr, Nd, and Tb). All four compounds order antiferromagnetically with the highest TN of 13 K for Tb3Au7Sn3. In Ce3Au7Sn3, which has a TN of 2.9 K, the heat capacity and electrical resistivity data in zero and applied fields indicate the presence of Kondo interaction. The coefficient of the linear term in the electronic heat capacity, γ, derived from the heat capacity data below 0.5 K is 211 mJ/Ce mol K2, suggesting strong electronic correlations due to the Kondo interaction. The electronic structure calculations based on the projector augmented wave method for particular representatives of the series suggest different tendencies of the localized R-4f atomic orbitals (AOs) to hybridize with the valence states. LMTO-based bonding analysis on the nonmagnetic La3Au7Sn3 indicates that the integrated crystal orbital Hamilton populations are dominated by the heteroatomic Au–Sn contacts; however, contributions from La–Au and La–Sn separations are significant, both together exceeding 40% in the overall bonding. Homoatomic Au–Au interactions are evident for the Au@Au6 units, but, despite of the high atomic concentration of Au in the compound, they do not dominate the entire bonding picture.