Triiodide and Other Rare-Earth Metal Triiodides

LANTHANUM TRIIODIDE (AND OTHER RARE EARTH METAL TRHODIDES) 

Submitted by JOHN D. CORBETT Checked by ARNDT SIMONf 

The reactions described below have been applied to the syntheses of the triiodides of the rare earth elements as well as those of yttrium and scandium. 

Lanthanum metal in the form of sheet, small lumps, or turnings should be stored under vacuum or inert gas and protected from the atmosphere as much as possible. (The reactivity of the rare earth metal decreases across the series so that the heavier members are relatively inert to air and moisture at room temperature.) These metals all form very stable carbides and hydrides, and degreasing may be necessary on the materials as received. 

The container is placed in the furnace slightly inclined so that the melt will cover the metal in the lower closed end, and the tube is heated for 12 48 hr at 300-330°. 

Lanthanum triiodide may be obtained from the oxide by a number of routes, such as dissolution of the oxide in Hl(aq) followed by precipitation of the 

The container for the Hglj-La reaction consists of a Pyrex tube 15-25 mm in diameter and 6-10 times as long. This is closed at one end, and the other end is connected to a ground-glass joint through a section of Pyrex tubing of 1.5-2 mm wall thickness, 6-10 mm i.d., suitable for seal-off under vacuum. 

---