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

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 not equal 0. Sn[PtBi6I12] crystallizes, isostructural to Pb[PtBi6I12], in the rhombohedral space group R3? 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 BiMIDLINE HORIZONTAL ELLIPSIS 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.

Automated summary

Through the combination of thermal and phase analyses of isothermal ex situ syntheses, a complex high-temperature synthesis protocol was established for the crystal growth of a target phase. This investigation also resulted in the discovery of a new subiodide with a complex structure and unique physical properties.