Lanthanide tribromides

First, the methods that apply to all three trihalides are reviewed then other specific methods are mentioned. Far fewer methods have been perfected for preparing anhydrous lanthanide tribromides than for the trichlorides, though most of them are similar. The triiodides are the most difficult to prepare, as the iodine analogs of several useful chloro and bromo sulfur and carbon compounds are not known. Reaction temperatures for preparation of triiodides have to be carefully controlled, as Sml3 and Ybl3, for example, decompose easily at elevated temperatures to diiodides. The existence of Eul3 is questionable, with EuI2 formed even at room temperature. 

High temperature heat capacity functions for the solid lanthanide tribromides ... 

Enthalpy of fusion and heat capacity of the liquid phase for the lanthanide tribromides and triiodides... 

The number of vapour pressure studies of the tribromides is significantly less. Gietmann et al. (1996) systematically measured the vaporization of the lanthanide bromides using mass spectrometry, showing the importance of the dimeric molecules in the vapour. For the light lanthanide tribromides (La, Ce, Nd) the fraction of dimers is around 0.01, but for TbBr3 it is 0.03,... 

Fig. 45. The enthalpies of dimerisation at 298.15 K of the lanthanide tribromides as derived from the work of Gietmann et al. (1996).

Experimental structural parameters and vibrational frequencies of the lanthanide tribromides bond distances in pm, bond angles in degrees, frequencies in cm... 

The trihalides MBr3 and MI3 are known for all the lanthanide elements. The early lanthanide tribromide (La to Pr) adopt the LaCh structure, while the later tribromides (from Nd to Lu) and the early triiodides (from La to Nd) form a layer structure with eight-coordinate lanthanide ions. 

Since this review was written, enthalpies of solution of several lanthanide tribromides in various concentrations of hydrochloric acid have been reported [C. Hurtgen, D. Brown, and J. Fuger, J. Chem. Soc. Dalton Trans, p. 70 (1980)]. 

The thermochemistry of rare-earth trifluorides was summarized in Gmelin Hand-buch (1976) and the thermochemistry of rare-earth tribromides and triiodides was summarized in Gmelin Handbuch (1978). The thermochemistry of trivalent rare-earth trichlorides was critically assessed by Morss (1976). Enthalpies of formation of most of the lanthanide tribromides were determined by Hurtgen et al. (1980). Thermodynamic properties for europium halides were assessed by Rard (1985). Only enthalpies of formation of Sc, Y, Dy and Tm triiodides have been redetermined since the classical work of Hohmann and Bommer (Morss and Spence 1992). A recent set of literature values of enthalpies of formation of rare-earth solid and gaseous trihalides has been published, accompanied by Born-Haber cycle estimated values for all trihalides (Struck and Baglio 1992). 

Grishin, A.E., Kryuchkov, A.S., Butman, M.F. et al. (2007) Suhlimation thermodynamics of some lanthanide tribromide. Proceedings of the 16th International Conference on Chemical Thermodynamics in Russia, Ivanovo, Rnssia, Vol. 1, p. 190. 

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