SrIr₉In₁₈ – A Structurally Complex Intermetallic Compound with Sr@Ir₄In₁₂, Ir@In₈ and Ir@In₉ Building Units

Abstract

Single crystals of SrIr9In18 were obtained by induction melting of the elements in a glassy carbon crucible followed by annealing at 1070 K. SrIr9In18 was structurally characterized by X‐ray powder and single crystal diffraction: P4m2, a = 811.21(5), c = 854.49(5) pm, wR2 = 0.0511, 1223 F2 values, and 46 variables. The structure is of a new type. The basic building units are Ir@In8 (distorted square‐prismatic, square anti‐prismatic and bicapped trigonal prismatic coordination) and Ir@In9 (distorted trigonal prismatic coordination) polyhedra, which condense to a three‐dimensional network, which leaves large cavities for the strontium cations, which are coordinated to four iridium and twelve indium atoms. The [Ir9In18]2– polyanionic network is stabilized through Ir–In (267–290 pm) and In–In (302–354 pm) bonding.

SrIrIn6 – An Intergrowth of SrIrIn4 with Indium Slabs

“…Such polyhedral building units have also been observed in the structures of SrIr 9 In 18 , [31] IrIn 2 , [2] and Yb 2 IrIn 8 . [11]…”

“…They have a tri-capped trigonal prismatic indium coordination with Ir-In distances ranging from 261 to 292 pm, comparable to the sum of the covalent radii [40] for Ir + In of 276 pm. Also the structures of SrIrIn 4 (261-288 pm), [19] BaIrIn 4 (260-290 pm), [20] and SrIr 9 In 18 (267-290 pm) [31] show similar ranges of Ir-In distances and one can safely ascribe strong covalent Ir-In bonding. This is underpinned by Z. Anorg.…”

“…These three polyhedra build up the whole structure. [31] IrIn 2 [2] and Yb 2 IrIn 8 ; [11] for details see text. The ninth indium neighbor of the Ir@In 9 polyhedron (yellow shading) of SrIrIn 6 is the center of the adjacent In@In 8 polyhedron (interpenetrating polyhedra).…”

“…[29] Also part of the Ba 2 Ir 4 In 13 [20] structure shows these building units, however, embedded in a more complex network, similar to BaIr 2 In 9 . [30] During our ongoing phase analytical work in the AE-T-In systems (T = electron-rich transition metal), we have recently characterized the complex intermetallic compound SrIr 9 In 18 [31] with the building units Sr@Ir 4 In 12 , Ir@In 8 and Ir@In 9 . In the indium-rich part of the same phase diagram we now obtained SrIrIn 6 which is a simple intergrowth variant of SrIrIn 4 [19] with indium slabs, forming a new structure type.…”