A new complex alkali metal aluminium amide borohydride, Li₂Al(ND₂)₄BH₄: synthesis, thermal analysis and crystal structure

Abstract

The mixtures of alkali metal aluminium amide MAl(ND2)4 and alkali metal borohydride MBH4 were synthesized using ballmilling. Thermal analysis and phase identifications of the MAl(ND2)4MBH4 system were performed by differential scanning calorimetry-thermogravimetric analysis, temperature programmed desorption-residual gas analysis, in-situ synchrotron radiation powder X-ray diffraction and Fourier transform Infrared spectroscopy. A previously unknown phase, Li2Al(ND2)4BH4, was formed in the samples of LiAl(ND2)4+2LiBH4 and NaAl(ND2)4+2LiBH4. Its crystal structure was solved and refined in the monoclinic space group P21/c, with a = 6.8582(3) Å, b = 11.3128(5) Å, c = 11.2117(4) Å,  = 124.186(5). Li2Al(ND2)4BH4 is the first reported compound containing both [Al(ND2)4] and BH4  anions. The ball-milling of NaAl(ND2)4+2NaBH4 and KAl(ND2)4+2KBH4 gave mixtures of the starting materials. The synthesized samples desorbed ammonia in the temperature range between 50 and 200 °C and hydrogen above ~300 °C.

Aluminium complexes of B- and N-based hydrides: Synthesis, structures and hydrogen storage properties

“…In particular, it would be interesting to characterize should also be explored. The first amide-borohydride containing aluminium, Li 2 (BH 4 )[Al(ND 2 ) 4 ], was reported during the revision of this manuscript [94]. Interestingly, Al 3þ coordinates only amides while the borohydride anions interact with the Li þ cation.…”