Complex Polyanionic Nets in RbAu_4.01(2)Ga_8.64(5) and CsAu₅Ga₉: The Role of Cations in the Formation of New Polar Intermetallics

Abstract

Single crystals of the new title compounds are prepared from the elements (Ta ampules, 300 °C, 7 d).

Layered Structures and Disordered Polyanionic Nets in the Cation-Poor Polar Intermetallics CsAu1.4Ga2.8 and CsAu2Ga2.6

“…The following temperature treatment has been applied for all samples: heat to 500 °C at 100 °C/h and keep at that temperature for 12 h, slowly cool to 300 °C at 5 °C/h, and quench in water. Single-crystals of CsAu 1.4 Ga 2.8 and CsAu 2 Ga 2.6 could always be found in mixtures with the previously reported , Cs 0.55 Au 2 Ga 2 , CsAu 5 Ga 9 , and a few compositionally close Au/Ga binary compounds as impurity components (Figure S1). The solutions and the refinements of the sets of single-crystal X-ray intensity data of specimens selected from different loadings revealed insignificant solid solutions for both compounds, expectable due to a number of disordered atomic positions with mixed Au/Ga occupancies (see below and Table ).…”

“…Despite the general importance of the geometric factors in this group of solids, predictions of the crystal structures based on anion-to-cation size ratio in polar intermetallics remains a challenge. The anionic constituent is, as a rule, surrounded by fewer atoms, 8–12, than the cationic, 16–24 or even 30 in the case of Cs; ,, yet, in many cases polyanionic networks can accommodate cations of considerably different sizes.…”

“…On the other hand, structural changes within the compositions A Au 3 Tr 2 , A Au 4 Tr 2 , or A Au 2 Ga 4 depend strongly on the selected cations and vary from minor distortion to completely different structure types. , While such systems with Na and K are well investigated and understood, those with Rb and especially Cs are largely unknown excluding a few common for all alkali metals isostructural specimens (Table ). The pioneering work in the Ga-rich area led to the discovery of two novel representatives RbAu 4.0 Ga 8.6 and CsAu 5 Ga 9 , uncovering the larger importance of the geometric factors in their structural stability . Due to good reactivity of Cs with Au and Ga more ternary phases could been expected to exist and finally were detected in the Ga-richer regions of the system.…”

Gold Polar Intermetallics: Structural Versatility through Exclusive Bonding Motifs

“…1−3 Since the relativistic orbital contraction affects mostly the s states, this is especially important for Au Cs 3 AuO, and Cs 9 Pt 4 H. 4−9 Following the tendency, the presence of Au in combination with some active and posttransition metals revealed its unique role in the stabilization of certain structure types known mainly for pnictides (Pn), where gold almost exclusively plays the role of the latter, i.e., and Pt, which also exhibit a special shell structure (5d m 6s n ). One of the most extreme outcomes of this combination is the formation of saltlike compounds with cesium: CsAu, Cs 2 Pt, 9 Au 5 −BaNi 9 As 5 , 10 Ae 2 Au 3 In 4 −Hf 2 Co 4 P 3 , 11 and AAu 4 In 6 − LiCo 6 P 4 (Ae = alkaline-earth metal, A = alkali metal). 12 On the other hand, Au was found to influence some active metals, leading to stable phases that otherwise were predicted to not exist: i-Na 13 Au 12 Ga 15 .…”

Crystal Structure and Bonding in BaAu5Ga2 and AeAu4+xGa3–x (Ae = Ba and Eu): Hexagonal Diamond-Type Au Frameworks and Remarkable Cation/Anion Partitioning in the Ae–Au–Ga Systems

“…For example, studies on Na (K)−Au−Ga and preliminary results with heavier alkali metals show that Na and K do not form compounds with a "cation"/"anion" ratio below 1:7, 3,20 whereas heavier "cations" allow smaller ratios, as low as 1:14, and are well separated by polyanionic frameworks. 25 No Sr/Ba−Au−Ga compounds have been reported until Ba 2 Au 6 (Au,Ga) 3 22 appeared within a family of isostructural compounds.…”