The Unprecedented Tetrakis‐(disulfato)‐silicate Anion [Si(S₂O₇)₄]⁴⁻, its Germanium Congener [Ge(S₂O₇)₄]⁴⁻, and the Tris‐(disulfato)‐metallates [M(S₂O₇)₃]²⁻ (M=Si, Ge, Ti), Stabilized by Divalent Counter Cations B²⁺ (B=Sr, Ba, Pb)

The reaction of oleum (65% SO(3)) with the tetrachlorides of silicon, germanium, and titanium, respectively, led to the complex disulfates Sr(2)[M(S(2)O(7))(4)] (M = Si, Ge), Ba[M(S(2)O(7))(3)] (M = Si, Ge, Ti) and Pb[M(S(2)O(7))(3)] (M = Ge, Ti) if strontium, barium, and lead were used as divalent counter cations. The strontium compounds exhibit the unique tetrakis-(disulfato)-metallate anions [M(S(2)O(7))(4)](4-) with the silicon and germanium atoms in octahedral coordination of two chelating and two monodentate disulfate groups. All of the other compounds display tris-(disulfato)-metallate anions [M(S(2)O(7))(3)](2-) with three chelating disulfate groups surrounding the M atoms. Thermoanalytical investigations on the germanium compounds Sr(2)[Ge(S(2)O(7))(4)] and Ba[Ge(S(2)O(7))(3)] revealed their decomposition in multi-step processes leading to a mixture of BSO(4) and BGe(4)O(9) (B = Sr, Ba), while the thermal degradation of Pb[Ti(S(2)O(7))(3)] yields PbTiO(3). For selected examples, IR data are additionally presented.