Europium trihalides, preparation

As already mentioned in the case of samarium and europium trihalides (Chervonnyi and Chervonnaya, 2007a,g), these compoimds have low enthalpies of sublimation and tend to decompose at high temperatures. Hastie et al. (1968) made an effort to stabilize the trivalent europium state. These authors prepared a mixture of europium and lutetium trichlorides, which melt at different temperatures (T = 894 K for EuCla and 1198 K for LuCla), and studied the composition of the vapor over this mixture by mass spectrometry. Data from the mass spectrum recorded at T = 960 K are presented in Table 49. At this temperature, the EuCla melt is... 

More care has to be taken for the preparation of binary chlorides and bromides, RCI3 and RBr3. The anhydrous salts are moisture-sensitive and they are obtained as (hepta- or hexa-) hydrates upon crystallization from hydrochloric or hydrobromic acid solutions. Simple dehydration of the hydrates in an HCl or HBr gas flow, respectively, appears to be possible (Seifert et al. 1985) but the less skfllliil chemist produces halide products more or less contaminated with oxyhahde, ROX. Sublimation of the raw product in an all-tantalum apparatus at higher temperatures (650 C to 950 C) and low pressures (10 bar) produces pure trihalides (with the exception of the rare-earth elements europium and 3dterbium where mixed-valent (+2/+3) or even dihalides are obtained under these conditions). 

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