|Molar mass||256.215 g/mol|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Iridium tetroxide (IrO4, Iridium(VIII) oxide) is a binary compound of oxygen and iridium in oxidation state +VIII.   This compound was formed by photochemical rearrangement of [(η1O2)IrO2] in solid argon at a temperature of 6 K (−267 °C, −449 °F). At higher temperatures the oxide is unstable. The detection of the iridium tetroxide cation by infrared photodissociation spectroscopy with formal oxidation state IX has been reported.  
- Gong, Yu; Zhou, Mingfei; Kaupp, Martin; Riedel, Sebastian (2009). "Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII". Angewandte Chemie International Edition 48 (42): 7879. doi:10.1002/anie.200902733.
- 20030138958, Blalock, Guy T., Micron technology, Inc., "Detection of gas phase materials", published 24-07-2003
- Citra, Angelo; Andrew, Lester (1999). "Reactions of Laser-Ablated Iridium Atoms with O2. Infrared Spectra and DFT Calculations for Iridium Dioxide and Peroxo Iridium(VI) Dioxide in Solid Argon". J. Phys. Chem. A 103 (21): 4182–4190. doi:10.1021/jp990388o.
- Himmel, D., Knapp, C., Patzschke, M. & Riedel, S. How far can we go? Quantum-chemical investigations of oxidation state IX. ChemPhysChem 11, 865–869 (2010) doi:10.1002/cphc.200900910
- Identification of an iridium-containing compound with a formal oxidation state of IX Guanjun Wang, Mingfei Zhou, James T. Goettel, Gary J. Schrobilgen, Jing Su, Jun Li, Tobias Schlöder & Sebastian Riedel Nature 514, 475–477 (23 October 2014) doi:10.1038/nature13795