R₃Au₉Pn (R = Y, Gd–Tm; Pn = Sb, Bi): A Link between Cu₁₀Sn₃ and Gd₁₄Ag₅₁

Abstract

A new series of intermetallic compounds RAuPn (R = Y, Gd-Tm; Pn = Sb, Bi) has been discovered during the explorations of the Au-rich parts of rare-earth-containing ternary systems with p-block elements. The existence of the series is strongly restricted by both geometric and electronic factors. RAuPn compounds crystallize in the hexagonal crystal system with space group P6/m (a = 8.08-8.24 Å, c = 8.98-9.08 Å). All compounds feature Au-Pn, formally anionic, networks built up by layers of alternating edge-sharing Au@Au and Sb@Au trigonal antiprisms of overall composition AuPn connected through additional Au atoms and separated by a triangular cationic substructure formed by R atoms. From a first look, the series appears to be isostructural with recently reported RAuSn (a ternary ordered derivative of the CuSn-structure type), but no example of RAuM is known when M is a triel or tetrel element. RAuPn also contains Au@AuAuR fully capped trigonal prisms, which are found to be isostructural with those found in the well-researched RAu series. This structural motif, not present in RAuSn, represents a previously unrecognized link between CuSn and GdAg parent structure types. Magnetic property measurements carried out for HoAuSb reveal a complex magnetic structure characterized by antiferromagnetic interactions at low temperature (T = 10 K). Two metamagnetic transitions occur at high field with a change from antiferromagnetic toward ferromagnetic ordering. Density functional theory based computations were performed to understand the materials' properties and to shed some light on the stability ranges. This allowed a better understanding of the bonding pattern, especially of the Au-containing substructure, and elucidation of the role of the third element in the stability of the structure type.

The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds

“…The crystal structure of the bismuth-containing intermetallic is derived from the MgCu 2 -type and constructed of networks of vertices-sharing gold tetrahedra enclosing the calcium and bismuth atoms. Notably, the structural motif of vertices-sharing gold tetrahedra has also been encountered for other types of polar intermetallics as, e.g., K 12 Au 21 Sn 4 [95,110] Furthermore, gold clusters have been identified for the crystal structures of R 3 Au 7 Sn 3 (R = Y, Gd) and Y 3 Au 9 Sb, in which the gold atoms assemble trigonal prisms and antiprisms enclosing extra gold and post-transition-metal atoms, respectively [97,100]. In the antimony-containing compound, the largest percentage contributions of the cumulative ICOHP per cell to the net bonding capabilities arise from the Au−Au interactions, while the largest shares of the cumulative ICOHP per cell to the total bonding capabilities in the tin-containing compounds stem from the Au−Sn separations (Table 2).…”

Gold Polar Intermetallics: Structural Versatility through Exclusive Bonding Motifs

“…Beside QCs and ACs, the systems with Au, triels, and light alkali metals (mostly Na) contain compounds exhibiting structural components with local fivefold symmetry icosahedra and polyicosahedral clusters, pentagonal bipyramids, and prisms (Table S3). Multiply endohedral clusters observed in K 34 Au 9 In 96 , Na 17 Au 6 Ga 47 , and Na 1.0 Au 0.2 Ga 1.8 ideally follow the first three shells of the classical Bergman-type sequence. The next shell, the M 60 buckyball-like polyhedron, surprisingly allows inclusion of the formal cation, Na.…”

“…Such a redistribution results in layers of edge-sharing Ga@Au 6 octahedra with maximal separation of Mg and Ga positions. Several modifications of this structural motif have been observed in a group of compounds including Yb 2 Au 3 Sn 2 , R 3 Au 4 Sn 3 , R 5 Au 8 Sn 5 , R 3 Au 7 Sn 3 , R 2 Au 5 Sn 2 , and R 3 Au 9 Pn 34. The three former compound series can be described with the general formula R Au Sn as an intergrowth of m…”

Compounds with Polar Metallic Bonding

“…The crystal structure of the bismuth-containing intermetallic is derived from the MgCu 2 -type and constructed of networks of vertices-sharing gold tetrahedra enclosing the calcium and bismuth atoms. Notably, the structural motif of vertices-sharing gold tetrahedra has also been encountered for other types of polar intermetallics as, e.g., K Au 21 Sn 4 [95,110] Furthermore, gold clusters have been identified for the crystal structures of R 3 Au 7 Sn 3 (R = Y, Gd) and Y 3 Au 9 Sb, in which the gold atoms assemble trigonal prisms and antiprisms enclosing extra gold and post-transition-metal atoms, respectively [97,100]. In the antimony-containing compound, the largest percentage contributions of the cumulative ICOHP per cell to the net bonding capabilities arise from the Au−Au interactions, while the largest shares of the cumulative ICOHP per cell to the total bonding capabilities in the tin-containing compounds stem from the Au−Sn separations (Table 2).…”