Synthesis and thermal decomposition of potassium tetraamidoboranealuminate, K[Al(NH2BH3)4]

A new potassium tetraamidoboranealuminate, K[Al(NH2BH3)(4)], has been synthesized by a mechanochemical reaction between KAlH4 and NH3BH3. The compound, K[Al(NH2BH3)(4)], crystallizes in a triclinic unit cell with space group symmetry P-1. The crystal structure consists of [K(NH2BH3)(6)](5-)octahedra which facilitate the bridging between K+ in 1D chains, while also bridging K+ to Al3+ to connect the 1D chains in a 3D network. Thermal analysis reveals that K[Al(NH2BH3)(4)] decomposes in two exothermic steps at T-94 and 138 C and releases primarily hydrogen. The total gas release amounts to-6.0 wt% H-2. The decomposition products are investigated ex situ by powder X-ray diffraction, infrared spectroscopy, and B-11 and Al-27 NMR and identified as KBH4 and amorphous phases, possibly BN3, N2BH, and/or NBH2 whereas aluminum is found in four-, five-, and six-fold coordination. Unfortunately, the decomposed sample shows no hydrogen absorption at T = 260 degrees C and p(H-2) = 110 bar. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.