Formation of Binuclear Platinum(III) Sulphates in Sulphic Acid Solutions of Platinum(IV) Compounds

The \({{({{\text{H}}_{3}}\text{O})}_{2}}[\text{Pt}_{2}^{\text{III}}{{(\text{S}{{\text{O}}_{4}})}_{4}}{{({{\text{H}}_{2}}\text{O})}_{2}}]\cdot 4{{\text{H}}_{2}}\text{O}\) compound (1) is isolated by keeping sulfuric acid solutions of the [Pt^IV(H₂O)₂(OH)₄] platinum hydroxide with an addition of 18-crown-6-ether. The structure of 1 (C2/c, a = 20.276(1) Å, b = 7.5844(5) Å, c = 13.8876(9) Å; β = 113.466(4)°; V = 1959.0(2) Å³; Z = 4) is determined by XRD and is shown to be formed by binuclear anionic platinum(III) aquasulfate complexes (containing bridging sulfate ligands and axial aqualigands), hydronium cations, and water molecules. The \({{({{\text{H}}_{3}}\text{O})}_{2}}[\text{Pt}_{2}^{\text{III}}{{(\text{S}{{\text{O}}_{4}})}_{4}}{{({{\text{H}}_{2}}\text{O})}_{2}}]\) (2) compound, containing no solvate water molecules, is prepared from a solution of the (Bu₄N)₂[Pt^IV(NO₃)₆] salt in strong sulfuric acid. The structure of 2 (P2₁, a = 7.4384(7) Å, b = 13471(1) Å, c = 7.566(1) Å; β = 101.419(4)°; V = 743.1(1) Å³; Z = 2), containing no solvate water molecules, is determined by XRD. The substances are characterized by Raman and NMR spectroscopy methods. The geometry of the \({{[\text{Pt}_{2}^{\text{III}}{{(\text{S}{{\text{O}}_{4}})}_{4}}{{({{\text{H}}_{2}}\text{O})}_{2}}]}^{2-}}\) anion is additionally calculated by the DFT method; the optimized model agrees well with structural data and confirms a presence of Pt–Pt bonding. Possible mechanisms of the formation of platinum(III) complexes in sulfate solutions of platinum(IV) compounds are discussed.