Thermal Decomposition Behavior of Hydrated Magnesium Dodecahydrododecaborates

MgB12H12 is an intermediate in the hydrogen desorption and sorption processes of magnesium borohydride, which is an important candidate material for hydrogen storage. It is thus highly desirable to synthesize anhydrous MgB12H12 in order to study its properties and its role in the hydrogenation and dehydrogenation of magnesium borohydride. Contrary to the literature claim, we find that anhydrous MgB12H12 cannot be obtained from simple thermal decomposition of Mg(H2O)(6)B12H12 center dot 6H(2)O (1) which has different thermal decomposition behavior from that of most hydrated alkali and alkaline earth salts of dodecahydrododecaborates. Thermal decomposition of 1 involves both dehydration and dehydrogenation processes in three steps, resulting in the formation of complexes Mg(H2O)(6)B12H12 (2), Mg(H2O)(6)B12H12 (3), and Mg(mu-OH)(x)B12H12-x, (4) that were characterized by XRD, IR, and B-11 NMR. Dehydrogenation was also confirmed by both the generation of hydrogen observed in TPD-MS spectra and the formation of polyhydroxylated complexes.