Crystal structures and thermal analyses of three new high-energy hydrazinium hydro-closo-borates

Abstract

New hydrazinium hydro-closo-borates with [BnHn]2– anions (n = 10 and 12) were obtained by direct reaction of the free acids (H3O)2[BnHn] with hydrazinium hydrate (N2H4 · x H2O) in aqueous solution. The three new compounds (N2H5)2[B10H10], (N2H5)2[B10H10] · 2 N2H4 and (N2H5)2[B12H12] · 2 N2H4 crystallize in the space groups P21/c, C2/c and P1‾, respectively. They contain up to 11 wt-% hydrogen. Two main kinds of bonding were observed in all crystal structures, classical hydrogen bonds (Nδ––Hδ+⋯Nδ–) and dihydrogen bonding between the negatively polarized hydrogen of the boron clusters and positively polarized hydrogen in hydrazinium cations (Bδ+–Hδ–⋯Hδ+–Nδ–). Thermal decomposition analyses of these compounds show that they absorb energy first, and then release a huge amount of energy upon decomposition and collapse of the structure. Due to the differently polarized hydrogen atoms in these compounds, hydrogen molecules (H2) are generated during the decomposition, which can be used as hydrogen fuel.