  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 trigonally
distorted skutterudite that consists of cooperatively tilted corner-sharing
IrSn3Se3 octahedra with ordered (Sn-Se)24- tetramers. Ir2SnSe5 is a layered,
distorted \b{eta}-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, 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,
non-spin-orbit split valence band, and suggest that Ir2Sn3Se3 is topologically
non-trivial under tensile strain, due to inversion of Ir-d and Se-p states.
