Proton Affinity in the Chemistry of Beta-Octamolybdate: HPLC-ICP-AES, NMR and Structural Studies

Abstract

The affinity of [β-Mo₈O₂₆]^4- toward different proton sources has been studied in various conditions. The proposed sites for proton coordination were highlighted with single crystal X-ray diffraction (SCXRD) analysis of (Bu₄N)₃[β-{Ag(py-NH₂)Mo₈O₂₆]}] (1) and from analysis of reported structures. Structural rearrangement of [β-Mo₈O₂₆]^4- as a direct response to protonation was studied in solution with ⁹⁵Mo NMR and HPLC-ICP-AES techniques. A new type of proton transfer reaction between (Bu₄N)₄[β-Mo₈O₂₆] and (Bu₄N)₄H₂[V₁₀O₂₈] in DMSO results in both polyoxometalates transformation into [V₂Mo₄O₁₉]^4-, which was confirmed by the ⁹⁵Mo, ⁵¹V NMR and HPLC-ICP-AES techniques. The same type of reaction with [H₄SiW₁₂O₄₀] in DMSO leads to metal redistribution with formation of [W₂Mo₄O₁₉]^2-.

Keywords: NMR; chromatography; octamolybdate; proton transfer; structural analysis.