Gallium Pnictides of the Alkaline Earth Metals, Synthesized by Means of the Flux Method: Crystal Structures and Properties of CaGa₂Pn₂, SrGa₂As₂, Ba₂Ga₅As₅, and Ba₄Ga₅Pn₈ (Pn = P or As)

Abstract

Keywords: Alkaline earth metals / Gallium / Pnictides / Solid-state structures / Density functional calculationsThe focus of this paper is on the structural characterization of the new Zintl phases CaGa 2 P 2 , CaGa 2 As 2 , SrGa 2 As 2 , and Ba 2 Ga 5 As 5 , and the solid solution (Ba 0.85(1) Sr 0.15 ) 2 Ga 5 As 5 , all of which were synthesized from molten metal fluxes. CaGa 2 P 2 , CaGa 2 As 2 , and SrGa 2 As 2 have layered structures with polyanionic layers made of ethane-like Ga 2 P 6 and Ga 2 As 6 motifs fused through common edges; the polyanionic substructure in Ba 2 Ga 5 As 5 consists of condensed Ga 2 As 6 units and GaAs 4 tetrahedra. Ba 4 Ga 5 P 8 and Ba 4 Ga 5 As 8 , another pair of new compounds with channel-like 3D structures, were also synthesized from metal fluxes, and their

New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

“…All reagents and products were handled within an argonfilled glove box with controlled oxygen and moisture level below 1 ppm. Single-crystals of Ba 7 Al 4 Sb 9 , and Ba 7 Ga 4 Pn 9 (Pn¼P, As) were first isolated from reactions attempted to extend the AETr 2 Pn 2 and AE 3 Tr 2 Pn 4 series [1][2][3] through use of the Al or Pb fluxes. Mixtures of the elements were loaded into alumina crucibles covered on the top with quartz wool and placed within fused silica tubes, which were then evacuated and flame-sealed.…”

“…Some years later, this seemingly trivial structure, based on layers of fused GaSb 4 tetrahedra, separated by Ba 2 þ cations, piqued the interest of Hoffmann and his group [14]. Two interesting structural features can be brought up for a discussion here: (1) the atypically long Sb-Sb bond; and (2), based on the valence rules, it seemed not possible to distribute the 14 electrons provided by the Ba atoms to the [Ga 4 Sb 9 ] polyanionic framework. Calculations based on the extended Hückel theory on [Ga 4 Sb 9 ] 14 À suggested localized bonding, and an extra electron located in an antibonding s* band pertaining to the 3.3 Å long Sb-Sb interactions (vide infra).…”

“…A variety of new ternary AE-Tr-Pn pnictides (AE¼Ca, Sr, Ba; Tr ¼Al, Ga, In; and Pn ¼P, As, Sb) have been reported in recent years, including BaGa 2 Pn 2 [1], Ba 2 Ga 5 As 5 , CaGa 2 Pn 2 , and SrGa 2 As 2 [2], AE 3 Al 2 Pn 4 and AE 3 Ga 2 Pn 4 [3], Ba 3 Al 3 Pn 5 and Ba 3 Ga 3 P 5 [4], discovered by our group, and BaGa 2 Sb 2 [5], Ba 3 Ga 4 Sb 5 [6], BaIn 2 P 2 [7], Ba 2 In 5 As 5 [8], among others, reported by teams from all over the world. In these compounds, significant differences in the electronegativities of the constituent elements imply complete electron transfer from electropositive alkaline-earth metals to (poly)anionic networks made up of electronegative metalloid elements, which form covalent bonds to attain closed-shell configuration.…”

Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

“…Since other groups had also explored the same ternary systems and had used the traditional solid-state synthesis methods [6][7][8][9][10][11][12], we focused our exploratory work aimed at new compounds and structures on the metal flux method [13,14]. After OPEN ACCESS all, the triel elements Ga and In are particularly well-suited for such endeavors, and we have applied this technique to grow crystals of many new phases [1][2][3][4][5][15][16][17][18][19][20].…”

“…Published examples from our prior work on the subject include BaGa2Pn2 (Pn = P, As) [16], CaGa2Pn2 (Pn = pnictogen, i.e., P, As) and SrGa2As2 [17], AE3Ga2Pn4 and AE3Al2Pn4 (AE = Ca, Sr, Ba, Eu and Yb; Pn = P, As) [18], Ba3Al3Pn5 (Pn = P, As, Sb) and Ba3Ga3P5 [19], Ba7Ga4Pn9 (Pn = P, As, Sb) [20], among others.…”