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

Abstract

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)2(4-) 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 Se(2-) 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 5d(6) Ir(3+). 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.

Structure, properties, and disorder in the new distorted-Hollandite PbIr4Se8

“…The 1-D channels in PbIr 4 Se 8 appear distorted in comparison to Hollandite, with Se-Se anion-anion bonding and a Se-Se bond distance of 2.50(2) Å in the smaller 1-D channels. This sort of anion-anion bonding is well known to occur in Ir chalcogenides [23,[34][35][36][37] and leads to a formal electron count of Pb 2+ (Ir 3+ ) 4 (Se 2 ) 2-(Se 2-) 6 , which is in good agreement with bond valence sums for an average Pb position (1.94 (2)), and the material exhibiting diamagnetic behavior (i.e. Ir is low-spin d 6 ).…”

“…The 1-D channels in PbIr 4 Se 8 appear distorted in comparison to Hollandite, with Se-Se anion-anion bonding and a Se-Se bond distance of 2.50(2) Å in the smaller 1-D channels. This sort of anion-anion bonding is well known to occur in Ir chalcogenides [23,[34][35][36][37] and leads to a formal electron count of Pb 2+ (Ir 3+ ) 4 (Se 2 ) ).…”

“…Though some non-oxide iridium chalcogenides have been studied, they are primarily derivatives of the binary compounds IrS 2 , IrSe 2 , and IrTe 2 . [19][20][21][22] Some recent work has been done on stoichiometric ternary Ir-Sn-Se compounds, [23,24] though none have yet looked at other stoichiometric ternary Ir-Se-X compounds.…”

“…oxide Ir-chalcogenides always appear to maintain Ir 3+ , from IrS 2 , IrSe 2 , IrTe 2 , to Ir 2 SnSe 5 , and more [23,[34][35][36][37]. These all have analogous portions of MnO 2 polymorphs, coupled with anion-anion bonding.…”

Copper Selenidophosphates Cu4P2Se6, Cu4P3Se4, Cu4P4Se3, and CuP2Se, Featuring Zero-, One-, and Two-Dimensional Anions

“…Interference of Debye and Einstein modes has also recently been connected to the presence of anion− anion bonds. 25 The thermal conductivity is 0.9 W/mK at room temperature (RT), the low value is most likely due to the low electronic conductivity since the Debye temperature is not particularly low, implying a significant phonon contribution to the thermal transport. The thermal conductivity is within the same range as the one of Cu 7 PSe 6 (0.2 W/mK).…”