# Thorium triiodide

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**Thorium triiodide** is a binary [inorganic compound](/source/Inorganic_compound) of [thorium](/source/Thorium) metal and [iodine](/source/Iodine) with the chemical formula ThI3.[1][2][3]

## Synthesis

Th metal is heated with [ThI4](/source/Thorium(IV)_iodide) in a vacuum at 800 °C.[4]

- Th + 3ThI4 → 4ThI3

## Physical properties

Thorium triiodide is a black, violet-tinged, usually poorly crystallized mass. Formed crystals exhibit strong [dichroism](/source/Dichroism) from violet to olive green under the microscope and are [birefringent](/source/Birefringence).[5] Above 550 °C, thorium(III) iodide decomposes to thorium(IV) iodide and thorium(II) iodide. *β*-thorium(III) iodide has an [orthorhombic crystal structure](/source/Orthorhombic_crystal_structure) with the space group *Cccm* (space group no. 66).[6] The *α*-form has a pseudoorthorhombic crystal structure.

## Chemical properties

ThI3 reacts with water to form thorium tetraiodide and thorium metal.[4]

## References

1. Yaws, Carl L. (6 January 2015). [*The Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals: Physical Properties for More Than 54,000 Organic and Inorganic Chemical Compounds, Coverage for C1 to C100 Organics and Ac to Zr Inorganics*](https://books.google.com/books?id=GutDBAAAQBAJ&dq=Thorium+triiodide&pg=PA802). [Gulf Professional Publishing](/source/Gulf_Professional_Publishing). p. 802. ISBN 978-0-12-801146-1. Retrieved 3 April 2024.

1. Brown, David; Canterford, J. H.; Colton, Ray (1968). [*Halides of the Transition Elements: Halides of the lanthanides and actinides, by D. Brown*](https://books.google.com/books?id=EHZMAAAAYAAJ&q=Thorium+triiodide). [Wiley](/source/Wiley_(publisher)). p. 229. ISBN 978-0-470-10840-6. Retrieved 3 April 2024.

1. Seaborg, Glenn T. (20 May 1994). [*Modern Alchemy: Selected Papers Of Glenn T Seaborg*](https://books.google.com/books?id=573sCgAAQBAJ&dq=Thorium+triiodide&pg=PA154). World Scientific. p. 21. ISBN 978-981-4502-99-3. Retrieved 3 April 2024.

1. David, Lore Rose (1953). [*Thorium: A Bibliography of Unclassified Literature*](https://books.google.com/books?id=Orhi3a-uEV0C&dq=Thorium+triiodide&pg=PA18). Technical Information Service. p. 18. Retrieved 3 April 2024.

1. Brauer, Georg (1975). [*Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume 1*](https://archive.org/stream/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/Handbook_of_Preparative_Inorganic_Chemistry_1__2_Brauer_djvu.txt). Stuttgart: Ferdinand Enke. p. 1142. ISBN 978-3-432-02328-1. Retrieved 19 June 2025.

1. Morss, Lester R.; Edelstein, Norman M.; Fuger, J. (2006). [*The Chemistry of the Actinide and Transactinide Elements*](https://link.springer.com/book/10.1007/1-4020-3598-5). Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). Springer. p. 78. [doi:10.1007/1-4020-3598-5](https://doi.org/10.1007/1-4020-3598-5). ISBN 978-94-007-0211-0. Retrieved 19 June 2025.

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Adapted from the Wikipedia article [Thorium triiodide](https://en.wikipedia.org/wiki/Thorium_triiodide) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Thorium_triiodide?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.