Preparation of anhydrous lanthanide halides, especially iodides

A general method is described which can be used to synthesize nearly all the lanthanide halides in high purity and good yield. It involves heating in vacuo, a molecularly dispersed mixture of hydrated lanthanide halide with the proper ammonium halide until the water and ammonium halide are expelled to leave pure, anhydrous lanthanide halide. All tri-halides except the iodides of samarium and europium are obtained. These are obtained as di-halides. Optimum condition for synthesis are discussed. The procedure is the only one which has been reported for preparing pure anhydrous iodides with relatively simple apparatus and technique.