The structural characterization of (NH_4)_2B_10H_10 and thermal decomposition studies of (NH_4)_2B_10H_10 and (NH_4)_2B_12H_12

摘要

The structure of (NH_4)_2B_10H_10 (1) was determined through powder XRD analysis. The thermal decomposition of 1 and (NH_4)_2B_12H_12 (2) was examined between 20 and 1000 ℃ using STMBMS methods. Between 200 and 400 ℃ a mixture of NH_3 and H_2 evolves from both compounds; above 400 ℃ only H_2 evolves. The dihydrogen bonding interaction in 1 is much stronger than that in 2. The stronger dihydrogen bond in 1 resulted in a significant reduction by up to 60 ℃, but with a corresponding 25% decrease in the yield of H_2 in the lower temperature region and a doubling of the yield of NH_3. The decomposition of 1 follows a lower temperature exothermic reaction pathway that yields substantially more NH_3 than the higher temperature endothermic pathway of 2. Heating of 1 at 250 ℃ resulted in partial conversion of B_(10)H_(10)~(2-) to B_(12)H_(12)~(2-). Both 1 and 2 form an insoluble polymeric material after decomposition. The elements of the reaction network that control the release of H_2 from the B_(10)H_(10)~(2-) can be altered by conducting the experiment under conditions in which pressures of NH_3 and H_2 are either near, or away from, their equilibrium values.