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Synthesis, Crystal Structure, and Thermal Properties of the First Mixed-Metal and Anion-Substituted Rare Earth Borohydride LiCe(BH4)3Cl

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posted on 01.12.2011, 00:00 by C. Frommen, M.H. Sørby, P. Ravindran, P. Vajeeston, H. Fjellvåg, B.C. Hauback
The mechanochemical reaction between LiBH4 and CeCl3 in a molar ratio of 3:1 has led to the formation of LiCe(BH4)3Cl. This compound is the first example of a mixed-metal and anion-substituted rare earth borohydride. The optimized structural parameters from total energy calculations based on DFT are in excellent agreement with the experimentally obtained data. The bonding interactions between constituents have been analyzed using charge density and partial density of states. The calculations suggest that LiCe(BH4)3Cl is an insulator. LiCe(BH4)3Cl crystallizes in the cubic space group I4̅3m (Z = 8) with lattice constant a = 11.5916(1) Å. It starts to decompose at ∼220 °C and forms CeH2 and amorphous boron containing species during dehydrogenation. The activation energy for the thermal decomposition was determined as 106(6) kJ/mol, and the material shows partial reversibility. Under 80 bar of hydrogen, 13% of the initial hydrogen content could be rehydrogenated at 340 °C.