Synthesis, Structure, and Bonding of Open-Shell Sr₃In₅:  An Unusual Electron Deficiency in an Indium Network, beyond the Zintl Boundary

Abstract

The new title compound has been synthesized and characterized by physical property measurements and electronic structure calculations. The results ratify the highly uncommon deficiency of one electron that has been long speculated for its Ca3Ga5-type structure on the basis of the simple Zintl electron counting formalism. In the Sr3In5 structure (Cmcm), 4- and 2-bonded indium atoms in a 4:1 ratio form a three-dimensional classical network that encapsulates strontium atoms in its narrow channels. The electrical conductivity of the compound shows typical metallic behavior. The detailed electronic structure analysis suggests that the electron hole is mainly localized on a nonbonding p-orbital on the 2-bonded indium atoms, and that these orbitals, stacked in a sigma-type way along avector (4.97 A), interact only weakly with each other to form highly one-dimensional bands.

On a TiNiSi‐Type Superstructure: Synthesis, Crystal and Electronic Structures of CaAgGe and Its Mn‐Substituted Derivative

“…At this point, it should be mentioned that several examples of phases with an open valence-shell are reported in the literature. [23][24] In general, such apparently electron short compounds with respect to the classical closed-shell bonding Scheme seems to develop when an interplay of other factors that govern the formation and stability of intermetallic compounds, like Madelung energy or packing efficiency, eventually overcome the usually dominant electronic effects. [25] In some case, a judicious adjustments of the bonding characteristics are realized using the flexibility of some peculiar subunits of the structure.…”

Novel intermetallics with the Ca11 Ga7 structure type

“…5 a), for the stoichiometric mixed triel/ tetrel compound Sr 11 [Al 4 ]Sn 3 slightly above this minimum and in Sr 10. 5 Pb 0.5 [In 4 ]Pb 3 only slightly below the minimum at 48 v.e./f.u..…”

“…increases, so do the values in both sites in nearly equal proportions: in Sr 11 Similar consequences of an incomplete electron transfer from the A cation to the M anion and of small deviations from ionic decomposition according to Zintl or (for more condensed M) Wade are not uncommon for binary trielides of the alkaline earths. Compounds such as Sr 5 In 3 [7], Sr 3 In 5 [5,32], Ca 2 In [7], BaIn [6] or Ba 3 Al 5 [21] show similar electron deficiency. Unoccupied states below the Fermi limit lead to small changes in M-M bond lengths, which can either increase or decrease, depending on the bonding or anti-bonding character of the depopulated states.…”

“…Most of these compounds have been characterized in 1980s [1,2], but the structures of some indides (although known for a long time [3,4]) have been solved only recently [5][6][7]. While most of the Ga/In-rich compounds with higher valence electron concentrations (v.e.c.)…”

Synthesis, structure and bonding of the hypoelectronic cluster compound Sr3Tl5

“…As examples of the former are isolated polyanionic clusters such as Tl 5 7 and Tl 9 9 in Na 2 K 21 Tl 19 [6], In 11 7 in K 8 In 11 [7], Tl 13 10 and Tl 13 11 , respectively, in Na 4 A 6 Tl 13 (A = K, Rb, Cs) and Na 3 K 8 Tl 13 [8], and Tl 5 7 , Tl 4 8 , Tl 3 7 and Tl 5 in Na 23 K 9 Tl 15.3 [9]. For the latter, a rich collection of more complex three-dimensional anionic networks, BaIn 4 [10], SrIn 4 [11], Sr 3 In 5 [12], BaTl 4 [13], BaIn 2 [14], etc. have been characterized.…”