Rubidium hydrazinidoborane: Synthesis, characterization and hydrogen release properties

In this work we present rubidium hydrazinidoborane RbN2H3BH3 (RbHB), the newest and last member of the alkali metal derivatives of hydrazine borane N2H4BH3 (HB). It is shown that HB readily reacts with metallic rubidium in THF at room temperature to form RbHB under argon atmosphere. The molecular and crystal structures of this new compound are discussed on the basis of FTIR spectroscopy, B-11 MAS NMR spectroscopy, and powder X-ray diffraction analyses. RbHB crystallizes in a monoclinic P2(1) (No. 4) unit cell where each Rb+ cation adopts octahedral coordination surrounded by six [N2H3BH3](-) anions, which are two more than for e.g. LiN2H3BH3 (with tetrahedral coordination) in accordance with the larger size of Rb+. RbHB is isostructural to potassium hydrazinidoborane KN2H3BH3. Its dehydrogenation properties, evaluated by using thermogravimetric analysis, differential scanning calorimetry, and isothermal analysis, are compared to those of the parent HB as well as to analogous compounds in order to evaluate the potential of RbHB as hydrogen storage material. According to the presented data, the dehydrogenation properties of RbHB are much better than those of HB and are comparable to those of the lithium derivative. Our main results are reported therein. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.