A New Complex Borohydride Lial(Bh4)(2)Cl-2

A new mixed alkali metal-aluminum borohydride LiAl(BH4)(2)Cl-2 has been prepared via mechanochemical synthesis from the 2LiBH(4)-AlCl3 mixture. Structural characterization, performed using a combination of X-ray powder diffraction and solid-state NMR methods, indicates that the LiAl(BH4)(2)Cl-2 phase adopts a unique 3D framework and crystallizes in an orthorhombic structure with the space group C222(1), a = 11.6709(6) angstrom, b = 8.4718(4) angstrom, c = 7.5114(3) angstrom. The material shows excellent dehydrogenation characteristics, where hydrogen evolution starts at Tons = 70 degrees C, releasing approximately 2 wt.% of nearly pure (99.8 vol.%) hydrogen and a very small amount (similar to 0.2 vol.%) of diborane. When compared to halide-free mixed alkali metal-aluminum borohydrides, the presence of Al-Cl bonding in the LiAl(BH4)(2)Cl-2 structure likely prevents the formation of Al(BH4)(3) upon decomposition, thus suppressing the formation of diborane.