Gold-rich R3Au7Sn3: establishing the interdependence between electronic features and physical properties

Two new polar intermetallic compounds Y3Au7Sn3 (I) and Gd3Au7Sn3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P6(3)/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au-6 antiprisms connected through R-3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au-6 prisms forming Au@Au-6 clusters with Au-Au distances of 2.906-2.960 angstrom, while the R-R contacts in the R-3 groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3Au7Sn3 shows an antiferromagnetic ordering at 13 K, while Y3Au7Sn3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3Au7Sn3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. Chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au-Gd and Au-Sn interactions, while homoatomic Au-Au bonding is evident within the Au@Au-6 clusters.