The preparation and crystallographic properties of certain lanthanide and actinide tribromides and tribromide hexahydrates

Abstract

Controlled vacuum thermal dehydration of lanthanide, actinide, and yttrium tribromide hexahydrates, MBr₃,6H₂O (M = Y, Pr, Nd, Gd—Lu incl., and U—Am incl.), gives the anhydrous tribromides. The tribromides of yttrium and of gadolinium to lutetium inclusive possess the rhombohedral ferric chloride type of structure, space group R(²C_3i). The tribromide hexahydrates possess monoclinic symmetry, space group P2/n. Unit cell dimensions are reported for both series of compounds and metal–bromine bond lengths have been calculated for the tribromides with the assumption of a perfect octahedral arrangement. The positions of the metal–bromine stretching vibrations are reported for selected compounds. The results are discussed in relation to possible structural changes in the series of actinide trihalides, MX₃(X = Cl, Br, or I).