Phasenbeziehungen im System Nain—Sn und die Kristallstrukturen der intermediären Verbindungen NaInSn2 und NaInSn4 / Phase Relations in the System Naln—Sn and the Crystal Structures of the Intermediate Compounds NaInSn2 and NaInSn4

Abstract

The quasibinary system Naln-Sn contains the intermediate phases NayInySn, Na9In9Sn2, NalnSn, Na2In2Sn3, NaInSn2 and NaInSn4. With the exception of Na2In2Sn3 (stable only between 134°C and 365°C), crystals of the ternary compounds were grown from the melt and were investigated by single crystal X-ray methods (Na9In9Sn: a = 2287.7(8) pm, F43m; Na9In9Sn2: a = 1662.4(7), c = 983.9(5) pm, P6/mmm; NaInSn: a = 486.1(2), c = 775.7(4) pm, P63/mmc; NaInSn2: a = 627.9(3), b = 654.3(3), c = 1139.6(5) pm, P212121; NaInSn4: a = 654.6(4), c = 531.6(6) pm, I4/mcm). The crystal structure of NaInSn is a representative of the Zintl-phases. with the [InSn]⁻-partial structure in a wurtzite-type arrangement. The crystal structures of NaInSn4 and NaInSn2 have been determined (R = 0.038 and 0.062, respectively). The crystal structure of NaInSn2 contains In and Sn atoms in a helical arrangement (six atoms per turn) along the α-axis direction. Interatomic bonds between neighbouring helices complete a distorted [2+2]-tetrahedral environment for every In/Sn position. The compound can be classified in terms of the Zintl concept. NaInSn4 is an isotype of the intermetallic phase Al2Cu. By this, the chemical and structural series NaInSn → NalnSn2 → NaInSn4 represents a change from Zintl-phases to an intermetallic phase.