Transformation of AeIn₄ Indides (Ae = Ba, Sr) into an AeAu₂In₂ Structure Type Through Gold Substitution

Abstract

The title compounds were prepared from the elements by high-temperature solid-state synthesis techniques. X-ray structural analyses shows that BaAu2In2 (1) and SrAu2In2 (2) crystallize in a new orthorhombic structure, Pnma, Z=4 (a=8.755(2), 8.530(2) A; b=4.712(1), 4.598(1) A; c=12.368(3), 12.283(4) A, respectively). Gold substitutes for 50% of the indium atoms in the tetragonal BaIn4 and monoclinic SrIn4 parents to give this new and more flexible orthorhombic structure. The Ae atoms in this structure are contained within chains of hexagonal prisms built of alternating In and Au that have additional augmenting atoms around their waists from further condensation of parallel displaced chains. The driving forces for these structural changes are in part the shorter Au-In distances (2.72 and 2.69 A) relative to d(In-In) in the parents, presumably because of relativistic contractions with Au. Generalities about such centered prismatic building blocks and their condensation modes in these and related phases are described. Band structure calculations (EHTB) demonstrate that the two compounds are metallic, which is confirmed by measurements of the resistivity of 1 and the magnetic susceptibilities of both.

Structural modification and optical reflectivity of new gold–indide intermetallic compounds

“…Levels of condensation and augmentations of the prisms depend on the concentration of the cation, molar ratio of Au to In, efficient packing, and the resulting valence electron concentration. Various molar ratios of strontium, gold, and indium show an incredible variety of condensation modes for polyanionic networks, especially with a low amount of strontium [1][2][3][4][5][6]. The dominant structural unit, the augmented hexagonal prisms encapsulating Sr atoms, share hexagonal faces and form channel-like structures along the shortest unit-cell axis direction, while exhibiting different levels of condensation along the two other longer unit-cell axes.…”

“…However, the coordination environment of Sr incorporates only 17 atoms within a reasonable near-neighbor distance of ∼4.01 Å, including 6 Au, 2 In, and 4 M atoms from the hexagonal prisms, and only 1 In and 4 M atoms from the waist 9-member ring. The interatomic distances between Sr and Au/In waist atoms fall in the range of ∼3.56 to ∼4.01 Å, listed in Table 3 tures in the Sr-Au-In system is driven by the efficient packing of each Sr cation to have as many close neighbors as possible [1][2][3][4]. The structures of the Ca and Ba analogues are structurally dissimilar, thus showing how critical the atomic size can be in the formation of their polyanionic networks.…”

“…The radii of the Wigner-Seitz (WS) spheres were assigned automatically so that the overlapping potentials would be the best possible approximations to the full potentials, and no interstitial sphere was necessary using the default 16% overlap restriction [16]. The WS radii determined by this procedure were reasonable: in the nominal 'SrAu3In5', 2.38 Å for Sr, 1 …”

“…The ternary gold-indide systems have revealed a wealth of novel Au-containing intermetallic compounds, and as well, have expanded our understanding of the structures of polar intermetallic compounds formed with electropositive alkaline-earth (Ae) metal and triel metals (Tr = Al-Tl) [1][2][3][4][5][6]. On the other hand, simpler elemental forms of gold have been studied for their potential in assisting solar energy conversion, such as in photocatalyst systems that absorb solar energy and use it to drive the production of chemical fuels.…”

Site-Preference among Three Anions in the Quaternary BaAl4-Type Structure: Experimental and Computational Investigations for BaLi1.09(1)In0.91Ge2

“…11,12 Moreover, numerous ternary phases with different substitutions for anionic elements have also been successfully synthesized, [13][14][15][16][17][18][19][20][21] and the site-preference of anions within the 3-dimensional (3D) frameworks has been thoroughly studied in terms of geometric-as well as electronic-perspectives. 11,13,14,21 However, the researches for the quaternary BaAl 4 -type phases containing an additional anion substitution in the polyanionic frameworks have been limited mostly for transition-metal [22][23][24] containing compounds due to the allowable range of electron counts between 12-14 to form the BaAl 4 -type structure.…”