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.

Anion-Anion Bonding and Topology in Ternary Iridium Seleno-Stannides. -IrSn 0.45Se1.55 (I), Ir2Sn3Se3 (II), and Ir2SnSe5 (III) are prepared by heating stoichiometric mixtures of the elements (silica tubes with 1-3 atm of Ar, 500 C) followed by repeated annealing at 950 C (I), 750 C (II), or 780 C (III). Small amounts of IrSe2 are observed in (II) and (III). Compound (I) is a pyrite phase which consists of tilted corner-sharing IrX 6 octahedra with randomly distributed (Sn-Se) 4and (Se-Se) 2dimers (space group Pa3, powder XRD). Compound (II) is a known trigonally distorted skutterudite that consists of cooperatively tilted corner-sharing IrSn3Se3 octahedra with ordered tetramers (rhombohedral space group R3). Compound (III) has a layered, distorted -MnO 2 (pyrolusite) structure consisting of a double IrSe6 octrahedral row, corner sharing in a direction and edge sharing in b direction (space group P2 1/m). This distorted pyrolusite contains (Se-Se) 2dimers and Se 2anions. Resistivity, specific heat, and magnetization measurements indicate insulating and diamagnetic behavior for all compounds. Electronic structure calculations on Ir 2Sn3Se3 reveal a single, spherical, non-spin-orbit split valence band. -(TRUMP*, B. A.; TUTMAHER, J. A.; MCQUEEN, T. M.; Inorg. Chem. 54 (2015) 24, 11993-12001, http://dx.doi.org/10.1021/acs.inorgchem.5b02387 ; Dep. Chem., Johns Hopkins Univ., Baltimore, MD 21218, USA; Eng.) -J. Schramke 08-020 (SnSe) 4-2