Design of High‐Temperature Syntheses on the Example of the Heavy‐Atom Cluster Compound Sn[PtBi₆I₁₂]

Abstract

Investigations into potential topological materials yielded the new subiodide Sn[PtBi6I12]. The combination of thermal analyses with phase analyses of the products of isothermal ex situ syntheses allowed the establishment of a complex high‐temperature synthesis protocol for the crystal growth of the target phase despite the lack of knowledge of the quaternary phase diagram. A special challenge was to prevent the formation of competing compounds of the solid solution series (Bi2xSn1–3x)[PtBi6I12] with x≠0. Sn[PtBi6I12] crystallizes, isostructural to Pb[PtBi6I12], in the rhombohedral space group Rtrue3‾ with lattice parameters a=1583.2(2) pm and c=1089.70(10) pm. The compound consists of cuboctahedral [PtBi6I12]2− clusters and Sn2+ cations in an octahedral coordination between the trigonal faces of two cluster units, thereby concatenating them into infinite linear chains. The chains are connected via Bi⋯ I inter‐cluster bridges, creating a high‐entropy variant of the NaCl structure type. Sn[PtBi6I12] is a semiconductor with an experimental bandgap of 0.8(1) eV. Fully relativistic density functional theory calculations including an implementation of the bifunctional formalism for the exchange energy indicate a topologically trivial bandgap of 0.81 eV between bands that are dominated by contributions of bismuth and iodine.