Amidoboranes of rubidium and caesium: the last missing members of the alkali metal amidoborane family

We report the synthesis and physicochemical characterization of two ammonia borane derivatives: rubidium amidoborane (RbNH2BH3) and caesium amidoborane (CsNH2BH3). Both compounds undergo solid-solid phase transition upon heating and then evolve pure hydrogen at temperatures lower than 125 [degree]C. The phase transition is clearly seen in the Raman spectra. We present crystal structures of both low- and high-temperature forms of the title compounds which were solved from powder X-ray data.