Crystal structure and thermal stability of monoclinic tetrahydrates of rare earth perrhenates

The structure of monoclinic rare earth perrhenates of the general formula of TR(ReO4)3 x 4H2O (TR=La - Pr) has been considered with lanthanum perrhenate tetrahydrate taken as an example. Thermal decomposition of the compounds has been analyzed in terms of crystal chemistry. A complete deciphering of the structure of lanthanum perrhenate monoclinic hydrate presents convincing evidence that four water molecules and not three are found in an elementary cell (and in a chemical formula) of the crystal