NMR Chemical Shifts of ¹¹B in Metal Borohydrides from First-Principle Calculations

Lightweight complex metal hydrides pose a challenge for experimental insight because of the lack of long-range order in the nanoconfined state or in intermediate phases. Understanding of the atomic scale properties might be the key to the utilization of complex hydrides in applications for versatile hydrogen storage. The first-principle calculations support of nuclear magnetic resonance methods applied to metal borohydrides is presented. We show that boron NMR chemical shifts can be accurately calculated within a density functional theory approach for a broad class of crystalline metal borohydrides. The calculated NMR parameters together with electronic and structural data provide detailed insight, on the atomic scale, into the properties of bulk and in particular of nanosized structures. It is explained that for small nanoclusters of LiBH₄, the boron chemical shift is low-frequency shifted because of lower coordination of ions compared to that of the bulk. The relation between Pauling electronegativity and boron chemical shift in metal borohydrides is proposed as a simple method for determining the stability of poorly crystalline materials