Preparation and characterization of bis(guanidinium) and bis(aminotetrazolium)dodecahydroborate salts: Green high energy nitrogen and boron rich compounds

Abstract

This paper describes the syntheses, crystallization, characterization and energetic properties (calorimetry) of closo-dodecahydroborate salts with guanidinium and aminotetrazolium based cations. The salts were readily produced in good yields by metathesis (ion exchange) reactions depending on the water solubility of the dodecahydroborate salts. Water insoluble salts can be synthesized from the potassium or sodium salts by a simple metathesis reaction with the corresponding halide of the desired organic cation. Water soluble salts can be prepared via two consecutive metathesis reactions: the halide is first converted to the corresponding sulfate, which is reacted in turn with barium dodecahydroborate, yielding the water soluble organic closo(B12H12)2− salt and the insoluble BaSO4. The product salt is conveniently isolated by water evaporation. The aminotetrazolium salt 12d gives nice crystals when recrystallized from DMF and NMP but incorporate solvent. Guanidinium salt 15a recrystallizes from nicely from water as a monohydrate. Thermogravimetric analyses established the thermal stabilities of these compounds. The enthalpies of combustion of representative salts were determined using a constant volume bomb calorimetry. The data shows that these salts possess relatively high heats of combustion (ΔUc, ca. 35 kJ·g−1), and have the potential to serve as green high-energy materials.