The honeycomb and hyperhoneycomb polymorphs of IrI${}_3$

The synthesis of IrI${}_3$ at high pressure in its layered honeycomb polymorph is reported. Its crystal structure is refined by single crystal X-ray diffraction. Faults in the honeycomb layer stacking are observed by single crystal diffraction, synchrotron powder diffraction, and transmission electron microscopy. A previously unreported hyperhoneycomb polymorph of IrI${}_3$ ($\beta$-IrI${}_3$), is also described. Its structure in space group Fddd is determined by single crystal XRD. Both materials are highly-resistive diamagnetic semiconductors, consistent with a low spin d${}^6$ configuration for Ir(III). The two- and three-dimensional Ir arrays in these polymorphs of IrI${}_3$ are analogous to those found in the $\alpha$- and $\beta$- polymorphs of Li${}_2$IrO${}_3$, although the Ir electron configurations are different.