New Energetic Dodecahydro-<i>closo</i>-Dodecaborates (N₂H₅)₄<i>X</i>₂[B₁₂H₁₂] (<i>X</i> = Cl and Br) with a Novel Hexagonal <i>A</i>₄<i>B</i>₂<i>C</i> Tunnel Stru

Two new tetrahydrazinium dihalide dodecahydro-closo-dodecaborates (N2H5)4X2[B12H12] (X– = Cl– and Br–) were successfully synthesized via the direct reaction of dihydrazinium dodecahydro-closo-dodecaborate (N2H4)2[B12H12] with hydrazinium halides (N2H5)Cl and (N2H5)Br in aqueous media. The resulting isotypic compounds crystallize monoclinically in the space group P21/c with similar unit-cell parameters (a = 681.98(4) pm, b = 1025.38(6) pm, c = 1325.38(8) pm, and β = 98.393(3)° for the chloride and a = 686.05(4) pm, b = 1032.51(6) pm, c = 1316.04(8), and β = 97.449(3)° for the bromide). Their crystal structure was elucidated using single-crystal X-ray diffraction techniques, unveiling a new unique arrangement for the composition A4B2C (A = hydrazinium, B = halide, and C = dodecahydro-closo-dodecaborate). This distinctive structural configuration sets it apart from compounds exhibiting other A4B2C arrangements, such as the spinel or double-perovskite structure type. In this new structure, the halide anions are coordinated by five hydrazinium cations, creating triangular bipyramidal polyhedra. These are interconnected via edge- and corner-sharing, resulting in the formation of hexagonal tunnels along the [100] direction. Within each of these tunnels, the [B12H12]2– clusters reside centrally located. Differential scanning calorimetry analyses demonstrate that these compounds contain a substantial amount of energy that is released during their thermal decomposition.