Iron and cobalt borohydrides stabilized by ammonia (NH3), [Fe(NH3)(6)](BH4)(2) and [Co(NH3)(6)](BH4)(2), were synthesized along with a solid solution, [Co(NH3)(6)](BH4)(2-x)Cl-x (x similar to 1), and a bimetallic compound, [Fe(NH3)(6)](Li-2(BH4)(4)). The compounds were prepared by new low-temperature, solvent-based synthesis methods, using dimethyl sulfide or liquid NH3, which allow for the removal of inert metal halides. The crystal structures were determined from synchrotron radiation powder X-ray diffraction (SR-PXD) data. [M(NH3)(6)](BH4)(2) (M = Fe, Co) and [Co(NH3)(6)](BH4)(2-x)Cl-x crystallize in the cubic crystal system, where the transition metals are octahedrally coordinated by NH3. Polymeric chains of lithium coordinated by four bridging BH4 anions are found in [Fe(NH3)(6)](Li-2(BH4)(4)). The new compounds have high hydrogen densities of similar to 14 wt % H-2 and similar to 140 g H-2/L and release a mixture of hydrogen and NH3 gas at low temperatures, T < 80 degrees C. The decomposition mechanisms of the prepared compounds along with the composites [Fe(NH3)(6)](BH4)(2)nNH(3)BH(3) (n = 2, 4, 6) were studied by thermal analysis and in situ SR-PXD.