Stabilizing Superacid Anions: The New [H(S4 O13 )2 ]3- Anion in the Crystal Structure of Li3 [H(S4 O13 )2 ].

The unique hydrogenium-bis-tetrasulfate anion [H(S4 O13 )2 ]3- in the crystal structure of Li3 [H(S4 O13 )2 ] (monoclinic, P21 /n (No. 14), Z=2, a=552.46(4) pm, b=939.70(6) pm, c=1876.6(1) pm, ß=97.492(3)°, V=965.9(1)⋅106  pm3 ) is the longest protonated polysulfate chain ever observed. Very strong symmetrical hydrogen bonds are a bold feature of the crystal structure. The protonation of a very weak base such as [S4 O13 ]2- and accordingly the stabilization of the first base of the superacid H2 S4 O13 is a significant success towards the still elusive polysulfuric acids.

Towards Polysulfuric Acids: The Hydrogentrisulfate Anion [HS3 O10 ]- in A[HS3 O10 ] (A=Na, K, Rb).

The reaction of Na2 SO4 and K2 SO4 with fuming sulfuric acid (65 % SO3 ) yielded colorless extremely sensitive crystals of Na[HS3 O10 ] (monoclinic; P21 /n (No. 14); Z=4; a=707.36(2), b=1378.56(4), c=848.10(3) pm; ß=94.817(1)°; V=824.09(4)⋅106  pm3 ) and K[HS3 O10 ] (orthorhombic; Pccn (No. 56); Z=4; a=1057.16(3), b=807.81(2), c=897.57(2) pm; V=766.51(3)⋅106  pm3 ). The analogous rubidium compound Rb[HS3 O10 ] (orthorhombic; Pnma (No. 62); Z=4; a=891.43(3), b=1095.34(4), c=839.37(3) pm; V=819.58(5)⋅106  pm3 ) originates from the reaction of Rb2 CO3 and SO3 . All of the different structures contain the hitherto unknown anion [HS3 O10 ]- and are stamped by strong hydrogen bonds linking the anions either to dimers or chains. Theoretical investigations by DFT methods give further insight in the structural characteristics of [HS3 O10 ]- . The preparation of the [HS3 O10 ]- anion can be seen as an important milestone on our way to the still elusive polysulfuric acids.

Polysulfates [Sn O3n+1 ]2- : With the [S6 O19 ]2- Anion, has the End been Reached?

The S6 O192- ion was obtained both as rubidium and ammonium salt from the reaction of the respective sulfate with SO3 . It is the largest polysulfate ion known to date and exhibits a chain of six vertex-connected [SO4 ] tetrahedra. The unique compound was comprehensively characterized and the bonding within the anion was elucidated by theoretical investigations.