Ba₅(Al/Ga)₅(Sn/Pb): Neue Verbindungen an der Zintl-Grenze / Ba₅(Al/Ga)₅(Sn/Pb): New Compounds at the Zintl Border

Abstract

The new isotypic intermetallic phases Ba 5 M III 5 M IV (M III = Al, Ga; M IV = Sn, Pb) have been synthesized from stoichiometric amounts of the elements at maximum temperatures of 900 to 1000 ◦C. They crystallize in the hexagonal space group P6̄m2 (Ba 5 Al 5 Sn: a = 605.05(8), c = 1109.0(2) pm, R1 = 0.0137; Ba 5 Ga 5 Sn: a = 599.45(5), c = 1086.00(7) pm, R1 = 0.0485; Ba 5 Al 5 Pb: a = 606.9(2), c = 1112.0(4) pm, R1 = 0.0409 and Ba 5 Ga 5 Pb: a = 601.76(7), c = 1091.51(13) pm, R1 = 0.0295), forming a new structure type. Similar to the Zintl phases Ba 2 M IV (Co 2 Si structure type, orthorhombic, space group Pnma; Ba 2 Sn: a = 861.52(14), b = 569.85(9), c = 1056.9(2) pm, R1 = 0.0217 and Ba 2 Pb: a = 865.12(13), b = 569.1(2), c = 1061.8(2) pm, R1 = 0.0470), these new ternary phases contain isolated M IV atoms (coordinated by 11 Ba atoms). In addition, sheets of 3- and 4-bonded Al/Ga atoms similar to those in Ba 3 Al 5 are present. In accordance with this, a formal subdivision of Ba 5 M III 5 M IV into Ba 3 M III 5 ・ Ba 2 M IV can be performed to describe the observed intergrowth or chemical twinning of two different binary intermetallics to give the new ternary compounds. Beyond structural aspects, also the nature of the chemical bonding (as studied by FP-LAPW calculations) in these new, non-electron precise compounds in the vicinity of the Zintl border can be interpreted in this vein.