Scandium triiodide, also known as scandium iodide, is an inorganic compound with the formula ScI3 Sometimes classified as a rare earth iodide, this compound is a yellowish powder.Haeberle, N., 1973, Preparation of highly pure lanthanide iodides, Technisch-Wissenschaftliche Abhandlungen der Osram-Gesellschaft, v. 11, p. 285 It is used in metal halide lamps together with similar compounds, such as caesium iodide, because of their ability to maximize emission of UV and to prolong bulb life. The maximized UV emission can be tuned to a range that can initiate photopolymerizations.Brabham, D.E., Metal halide lamp for curing adhesives. U.S. Patent 6,888,312, March 1, 2011
Scandium triiodide adopts a structure similar to that of iron trichloride (FeCl3), crystallizing into a rhombohedral lattice. Scandium has a coordination number of 6, while iodine has a coordination number of 3 and is trigonal pyramidal.Men'kov, A. A., Komissarova, L. N., 1964, X-ray study of scandium iodide, Zhurnal Neorganicheskoi Khimii, v. 9, p. 766
High purity scandium triiodide is obtained through direct reaction of the elements: 2 Sc + 3 I2 → 2 ScI3 Alternatively, but less effectively, one can produce anhydrous scandium triiodide by dehydrating ScI3(H2O)6.
The octahydrate is also known: formula ScI3(H2O)8.
Further information Tomasz Mioduski, Cezary Gumiski, and Dewen Zeng "Rare Earth Metal Iodides and Bromides in Water and Aqueous Systems. Part 1. Iodides" Journal of Physical and Chemical Reference Data 2012, vol. 41, 013104-1 to 013104-63.
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