NMR confirmation for formation of [B12H12]2- complexes during hydrogen desorption from metal borohydrides

B-11 NMR spectroscopy has been employed to identify the reaction intermediates and products formed in the amorphous phase during the thermal hydrogen desorption of metal tetrahydroborates (borohydrides) LiBH4, Mg(BH4)(2), LiSc(BH4)(4), and the mixed Ca(AIH(4))(2)-LiBH4 system. The B-11 magic angle spinning (MAS) and cross polarization magic angle spinning (CPMAS) spectral features of the amorphous intermediate species closely coincide with those of a model compound, closo-borane K2B12H12 that contains the [B12H12](2-) anion. The presence of [B12H12](2-) in the partially decomposed borohydrides was further confirmed by high-resolution solution B-11 and H-1 NMR spectra after dissolution of the intermediate desorption powders in water. The formation of the closo-borane structure is observed as a major intermediate species in all of the metal borohydride systems we have examined.