Neue gemischte Sr/Ba-Trielide AIIInxMIII 1– x (M = Ga, Al)

Abstract

A series of new ternary mixed Sr and Ba trielides of overall composition 1 : 1 was synthesized from stoichiometric quantities of the elements. The structures of the new compounds were determined using single crystal X-ray data. In the case of the Sr compounds, commensurately modulated new superstructures of the CrB type are formed in the In-rich part of the ternary system SrAl - SrGa - SrIn: The gallides, SrIn1−xGax (x = 0.30, orthorhombic, space group Ima2, a = 1954.2(7), b = 1305.6(4), c = 1272.6(3) pm, Z = 48, R1 = 0.0848) are formed in the composition range x = 0.20 to 0.30. The closely related aluminide SrIn1−xAlx (x = 0.04, orthorhombic, space group Pnna, a = 1280.1(7), b = 1482.0(5), c = 1308.7(5) pm, Z = 36, R1 = 0.1164) and the isotypic Zn compound SrIn0.90Zn0.10 (a = 1277.7(4), b = 1489.9(3), c = 1301.3(4) pm, R1 = 0.0629) also contain mainly In as the triele element. The structures, similar to CrB, contain zig-zag chains of two-bonded In-Ga/Al, in which the ordering of the trieles results in a strong wavelike form of the originally planar zig-zag chains. In contrast, no corresponding Ba compounds were formed. Instead, BaIn0.46Ga0.54 (triclinic, space group P1̄, a = 661.1(3), b = 679.4(2), c = 712.4(3) pm, α = 69.13(3), β = 77.14(3), γ = 84.27(3)°, Z = 2, R1 = 0.0557) crystallizes with a new structure type and exhibits a planar rhomb-like anion with both two- and three-bonded In/Ga atoms. Attempts to obtain 1 : 1 compounds in-between BaAl and BaIn resulted in the formation of the 5 : 6 phases Ba5In6−xAlx (x = 4.1/5.1, hexagonal, space group P6̄m2, a = 612.2(4)/608.6(1), c = 1124.6(10)/1116.80(6) pm, Z = 1, R1 = 0.0608/0.0147) which are isotypic to Ba5M5 IIIMIV (MIII = Al, Ge; MIV = Sn, Pb). Their structures contain isolated In anions (coordinated by 11 Ba atoms) and sheets of 3- and 4-bonded Al/In atoms similar to those known from the structures of Ba aluminides like Ba3Al5.