Nuclear Magnetic Resonance Studies of BH4 Reorientations and Li Diffusion in LiLa(BH4)(3)Cl

To study the reorientational motion of BH4 groups and the translational diffusion of Li+ ions in the novel bimetallic borohydride chloride LiLa(BH4)(3)Cl, we have measured the H-1, B-11, and Li-7 NMR spectra and spin-lattice relaxation rates in this compound over the temperature range of 23-418 K. At low temperatures (T < 110K), the proton spin-lattice relaxation rates are governed by fast reorientations of BH4 groups. This reorientational process can be satisfactorily described in terms of a two-peak distribution of the activation energies with the peak E-a values of 41 and 50 meV. Above 200 K, the NMR data are governed by a combined effect of two types of motion occurring at the same frequency scale: Li ion diffusion and another (slower) reorientational motion of BH4 groups. These results suggest that the Li ion jumps and the slower reorientational jumps of BH4 groups in LiLa(BH4)(3)Cl may be correlated. The estimate of the tracer Li ion diffusion coefficient at room temperature (5.2 X 10(-8) cm(2)/s) following from our experimental data indicates that LiLa(BH4)(3)Cl can be considered as a promising solid-state ionic conductor.