SrAu₄In₄ and Sr₄Au₉In₁₃: Polar Intermetallic Structures with Cations in Augmented Hexagonal Prismatic Environments

Abstract

The title compounds were synthesized via high-temperature reactions of the elements in welded Ta tubes and characterized by single-crystal X-ray diffraction analyses and band structure calculations. SrAu(3.76(2))In(4.24) crystallizes in the YCo5In3 structure type with two of eight network sites occupied by mixtures of Au and In: Pnma, Z = 4, a = 13.946(7), b = 4.458(2), c = 12.921(6) A. Its phase breadth appears to be small. Sr4Au9In 13 exhibits a new structure type, P_6 m2, Z = 1, a = 12.701(2), c = 4.4350(9) A. The Sr atoms in both compounds center hexagonal prisms of nominally alternating In and Au atoms and also have nine augmenting (outer) Au + In atoms around their waists so as to define 21-vertex Sr@Au9M4In8 (M = Au/In) and Sr@Au9In12 polyhedra, respectively. The relatively larger Sr content in the second phase also leads to condensation of some of the ideal building units into trefoil-like cages with edge-shared six-member rings. One overall driving force for the formation of these structures can be viewed as the need for each Sr cation to have as many close neighbors as possible in the more anionic Au-In network. The results also depend on the cation size as well as on the flexibility of the anionic network and an efficient intercluster condensation mode as all clusters are shared. Band structure calculations (LMTO-ASA) emphasize the greater strengths (overlap populations) of the Au-In bonds and confirm expectations that both compounds are metallic.

Complex Intermetallic Compounds: CaNi5Ge3, Ca15Ni68Ge37, and Ca7Ni49Ge22 – Three Multifaceted Ni‐Ge Framework Structures Combining the Structural Motifs of Ni3Ge and CaNi2Ge2

“…In all cases the differentiation of the elements, with relatively similar valence electrons to Ge and Ni, is undoubtedly possible. In CaNi 5 Ge 3 and Ca 15 Ni 68 Ge 37 no disorder is observed. Ca 7 Ni 48.9(4) Ge 22.1 (4) , however, showed a mixed occupancy of Ni and Ge on one specific site.…”

“…The crystal structure of CaNi 5 Ge 3 can be described as a combination of the structural motifs of CaNi 2 Ge 2 (ThCr 2 Si 2 structure type) [28] and Ni 3 Ge [29] (AuCu 3 structure type) [30] . Both of the motifs are also found in the two further title compounds, Ca 15 Ni 68 Ge 37 and Ca 7 Ni 48.9(4) Ge 22.1 (4) . The resulting building blocks, namely, the Ca-centered condensed hexagonal prisms of the Ni and Ge atoms, can be discussed in the context of the structures mentioned above.…”

“…A variation of the stoichiometry resulted in the formation of three new intermetallic compounds. The structures and compositions of the compounds CaNi 5 Ge 3 , Ca 15 Ni 68 Ge 37 , and Ca 7 Ni 48.9(4) Ge 22.1 (4) were determined by single-crystal X-ray diffraction methods. In all cases the differentiation of the elements, with relatively similar valence electrons to Ge and Ni, is undoubtedly possible.…”

“…Furthermore, some indides of the systems R/ T/In (R = Ca, Sr, Eu; T = Au, Pt), which contain capped hexagonal prisms as coordination polyhedra of R, have been reported. [14][15][16] The comparatively small and constant c axis (about 3.7 Å) is common to all of the structure types and corresponds to the height of a hexagonal prism. In contrast, the a and b axes increase with the complexity of the linkage of the hexagonal prisms.…”

“…Further research led to the discovery of the title compounds CaNi 5 Ge 3 , Ca 15 Ni 68 Ge 37 , and Ca 7 Ni 48.9(4) Ge 22.1 (4) , each of which crystallized in a new structure type. The crystal structure of CaNi 5 Ge 3 can be described as a combination of the structural motifs of CaNi 2 Ge 2 (ThCr 2 Si 2 structure type) [28] and Ni 3 Ge [29] (AuCu 3 structure type) [30] .…”