Synthesis, structural analysis, and thermal decomposition studies of [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8)

Boron-nitrogen containing compounds with high hydrogen contents as represented by ammonia borane (NH sub(3)BH sub(3)) have recently attracted intense interest for potential hydrogen storage applications. One such compound is [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8) with a capacity of 18.2 wt% H. Two safe and efficient synthetic routes to [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8) have been developed for the first time since it was discovered 50 years ago. The new synthetic routes avoid a dangerous starting chemical, tetraborane (B sub(4)H sub(10)), and afford a high yield. Single crystal X-ray diffraction analysis reveals N-H super() delta ..H super() delta B dihydrogen interactions in the [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8).18-crown-6 adduct. Extended strong dihydrogen bonds were observed in pure [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8) through crystal structure solution based upon powder X-ray analysis. Pyrolysis of [(NH sub(3)) sub(2)BH sub(2 )]B sub(3)H sub(8) leads to the formation of hydrogen gas together with appreciable amounts of volatile boranes below 160 degree C.