Experimental evidence of Na<inf>2</inf>[B<inf>12</inf>H<inf>12</inf>] and Na formation in the desorption pathway of the 2NaBH<inf>4</inf> + MgH <inf>2</inf> system

In the present work we report the desorption pathway of the 2NaBH 4 + MgH2 system. Ex-situ X-ray powder diffraction (XRPD) and solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) measurements have been performed on samples heat treated up to 450 °C for different times. Ex-situ X-ray powder diffraction experiments conducted on fully desorbed samples allowed us to identify nanocrystalline MgB2 and metallic Na as dehydrogenation products. 11B and 23Na NMR analyses have been also carried out in order to evaluate the structural evolution of decomposed materials. Our measurements show that the local structure of MgB2 is influenced by replacement of Mg with Na atoms in the Mg sites. Moreover, amorphous Na2[B12H12] was detected in the partially desorbed sample and in the final products of the decomposition reaction. The presence of the [B12H12] 2- anion was confirmed by both direct comparison with the 11B{1H} NMR spectrum of pure Na2[B 12H12] and dynamic cross-polarization experiments. © 2011 American Chemical Society.