The Molecular Structures of Lithium Trichlate, Li[Cl3CSO3]⋅2H2O, and Lithium Tribrate, Li[Br3CSO3]⋅2H2O

The bigger siblings of the triflate anion, namely the trichlate [Cl₃CSO₃]⁻ and the tribrate [Br₃CSO₃]⁻ are synthesized as their lithium salts. The compounds display molecular structures with the anions, the lithium cations and water molecules arranged into dimers [Li₂(X₃CSO₃)₂(H₂O)₄] (X=Cl, Br). The figure shows both dimers, partly in an ORTEP style and partly as a Lewis formula.

Abstract

Lithium trichlate, Li[Cl₃CSO₃] ⋅ 2H₂O (triclinic, , Z=2, a=630.29(3) pm, b=630.65(3) pm, c=1246.10(6) pm, α=100.657(2)°, β=97.813(2)°, γ=107.994(2)°) was obtained from the reaction of (H₅O₂)[Cl₃CSO₃] and LiOH in aqueous solution. Similarly, colourless single crystals of the tribrate Li[Br₃CSO₃] ⋅ 2H₂O (triclinic, , Z=4, a=634.65(4) pm, b=636.83(4) pm, c=2496.8(2) pm, α=83.518°, β=86.081(5)°, γ=72.061(5)°) form in the reaction of aqueous Br₃CSO₃H and LiOH. The acid (H₅O₂)[Cl₃CSO₃] was obtained from the chlorination of CS₂, followed by oxidation of the intermediate Cl₃CSCl with H₂O₂. The bromo derivative Br₃CSO₃H has been prepared by bromination of phenylsulfonate with KOBr and subsequent ion exchange of the obtained potassium salt. Both lithium compounds exhibit molecular dimers according to {Li₂(X₃CSO₃)_2/1(H₂O)_2/1(H₂O)_2/2} with the Li⁺ ions in tetrahedral coordination of oxygen atoms. The difference in the crystal structures result from the variation of the orientation of the dimers with respect to each other. The experimental findings for the dimers are in good agreement with DFT calculations.

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