Synthesis and Characterization of the First Borosulfates of Magnesium, Manganese, Cobalt, Nickel, and Zinc

The first magnesium, manganese, cobalt, nickel, and zinc borosulfates were synthesized employing solvothermal conditions starting from the superacid H­[B­(HSO4)4] and the respective metal powders (Mg, Ni, Zn) or oxides (MnO2, CoO). α-M 4[B2O­(SO4)6] (M = Mg, Mn, Co, Ni, Zn) crystallize isotypically in a new structure type in P3̅ (No. 147) with Z = 1, a = 793.59(4)–810.86(9) pm, and c = 743.98(4)–775.09(9) pm. The oligomeric anion comprises unprecedented dimeric open-branched quadruple tetrahedra { oB , 4 t }­[B2O­(SO4)6]8–, which are connected via M 2O9 dimers to give a three-dimensional network. Upon mild heating, we observed a phase change from α-Mg4[B2O­(SO4)6] to β-Mg4[B2O­(SO4)6], yielding a further new structure type in P3̅ (No. 147) with Z = 3, a = 1391.96(6) pm, and c = 748.54(3) pm. The reaction of MgB2 with SO3 yields Mg­[B2(SO4)4] crystallizing in C2/c with Z = 4, a = 1744.28(10) pm, b = 531.45(3) pm, c = 1429.06(8) pm, and β = 126.323(2)° showing phyllosilicate topology. UV/vis spectroscopy on α-TM 4[B2O­(SO4)6] (TM = Co, Ni) confirms the valence state of the TM and reveals that borosulfates are weakly coordinating host structures. Structure relationships between the presented crystal structures and similar borophosphates are shown. The results of vibrational spectroscopy as well as magnetic and thermal measurement investigations are discussed.