Anion–Anion Bonding and Topology in Ternary Iridium Seleno–Stannides

The
synthesis and physical properties of two new and one known Ir–Sn–Se
compound are reported. Their crystal structures are elucidated with
transmission electron microscopy and powder X-ray diffraction. IrSn0.45Se1.55 is a pyrite phase which consists of tilted
corner-sharing IrX6 octahedra with randomly
distributed (Sn–Se)4– and (Se–Se)2– dimers. Ir2Sn3Se3 is a known trigonally distorted skutterudite that consists of cooperatively
tilted corner-sharing IrSn3Se3 octahedra with
ordered (Sn–Se)24– tetramers.
Ir2SnSe5 is a layered, distorted β-MnO2 (pyrolusite) structure consisting of a double IrSe6 octrahedral row, corner sharing in the a direction
and edge sharing in the b direction. This distorted
pyrolusite contains (Se–Se)2– dimers and
Se2– anions, and each double row is “capped”
with a (Sn–Se)n polymeric chain.
Resistivity, specific heat, and magnetization measurements show that
all three have insulating and diamagnetic behavior, indicative of
low-spin 5d6 Ir3+. Electronic structure calculations
on Ir2Sn3Se3 show a single, spherical, nonspin–orbit split valence band and suggest that
Ir2Sn3Se3 is topologically nontrivial
under tensile strain due to inversion of Ir-d and Se-p states.