Crystal structure and in situ decomposition of Eu(BH4)2 and Sm(BH4)2

Abstract

Synthesis of halide free rare earth metal (RE) borohydride complexes is demonstrated by the metathesis reaction of trivalent RE metal chlorides and LiBH₄ in ethereal solution, combined with solvent extraction using dimethyl sulfide. The crystal structures of Eu(BH₄)₂ and Sm(BH₄)₂ are orthorhombic (space group Pbcn) and are shown to be related to the structure of Sr(BH₄)₂ by Rietveld refinement. Further, the thermal decomposition of these materials has been studied by in situ synchrotron radiation powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and Sieverts measurements. The decomposition pathway of these solvent extracted materials has been compared against materials prepared by mechano-chemistry, the process of which is simplified by the absence of chloride impurities.