Synthesis, Characterization, and Atomistic Modeling of Stabilized Highly Pyrophoric Al(BH_4)_3 via the Formation of the Hypersalt K[Al(BH_4)_4]

Abstract

The recent discovery of a new class of negative ions called hyperhalogens allows us to characterize this complex as belonging to a unique class of materials called hypersalts. Hyperhalogen materials are important while serving as the building blocks for the development of new materials having enhanced magnetic or oxidative properties. One prime example of a hydperhalogen is the Al(BH_4)_4^– anion. Aluminum borohydride (17 wt % H) in itself is a volatile, pyrophoric compound that has a tendency to release diborane at room temperature, making its handling difficult and very undesirable for use in practical applications. Here we report that the combination of Al(BH_4)_3 with the alkaline metal borohydride KBH_4 results in the formation of a new compound KAl(BH_4)_4 which is a white solid that exhibits remarkable thermal stability up to 154 °C and has the typical makeup of a hypersalt material. Using a variety of characterization tools and theoretical calculations, we study and analyze the physical characteristics of this compound and show its potential for stabilizing high hydrogen capacity, energetic materials.

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