The honeycomb and hyperhoneycomb polymorphs of IrI$_3$

TL;DR

This study reports the synthesis, structural characterization, and properties of layered honeycomb and hyperhoneycomb polymorphs of IrI$_3$, revealing their unique crystal structures and diamagnetic semiconducting behavior.

Contribution

It introduces a new hyperhoneycomb polymorph of IrI$_3$ and provides detailed structural analysis of both polymorphs, expanding understanding of IrI$_3$ crystal chemistry.

Findings

Both polymorphs are highly-resistive diamagnetic semiconductors.

Faults in layer stacking are observed in the honeycomb form.

The hyperhoneycomb structure is newly reported and characterized.

Abstract

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.