Neodymium(III) chloride



 Neodymium(III) chloride, also known as neodymium trichloride, is NdCl3. This anhydrous compound is a mauve-coloured solid that rapidly absorbs water on exposure to air to form a purple-coloured hexahydrate, NdCl3.6H2O (CAS number 13477-89-9, density 2.282 g cm-3). This hydrate, like many neodymium salts, has the interesting property that it loses its colour under fluorescent light (see picture)- it also appears jet-black under a sodium light as well. The hydrate is soluble in water to the extent of 0.967 kg/L at 13°C [2]. NdCl3 is soluble (0.445 kg/L) in ethanol but insoluble in chloroform and ether[2]. The anhydrous salt features Nd in a nine-coordinate tricapped trigonal prismatic geometry and crystallises with the UCl3 structure[1].

Preparation of anhydrous NdCl3
Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis [1], although the method given for drying cerium(III) chloride heptahydrate would be expected to work also for NdCl3.6H2O. Anhydrous NdCl3 can also be made by dehydration of the hydrate either by slowly heating to 400 °C with 4-6 equivalents of ammonium chloride under high vacuum[1],[4], or by heating with an excess of thionyl chloride for four hours.[1],[5] The anhydrous halide may alternatively be prepared from neodymium metal and hydrogen chloride.[6]  It is usually purified by high temperature sublimation under high vacuum. [1]

Uses
There are no major uses for neodymium(III) chloride, other than the manufacture of neodymum metal by electrolysis, though it can be used as a starting point for the preparation of other neodymium salts. One commercial supplier of the material to schools recommends NdCl3 as "Great solution for teaching absorption spectroscopy. Violet color provides a good line spectrum." NdCl3 has also been used (in combination with triethylaluminium and 2-propanol) as a catalyst in the polymerisation of 1,3-butadiene.[7]