Synthesis, spectra and structure characterization of organic ammonium paratungstates

Abstract

Dissolution of tungstic acid in aqueous organic amine (RNH₂ where R = methyl or ethyl, or n-propyl or isopropyl, n-butyl, t-butyl etc.) results in the formation of the tetrahedral tetraoxidotungstate(VI) species in solution. Slow evaporation of the reaction mixture to isolate tetraoxidotungstates charge balanced by organic ammonium cations afforded organic ammonium paratungstates having  formula (RNH₃)₁₀[H₂W₁₂O₄₂]·xH₂O. The presence of [WO₄]^2- species in solution and the [H₂W₁₂O₄₂]^10- unit in the solid product is confirmed by the characteristic Raman spectra. In this report, we describe the synthesis, Raman spectra, crystal structures and properties of two organic ammonium paratungstates viz. (MeNH₃)₁₀[H₂W₁₂O₄₂]·12H₂O 1 (MeNH₂ = methylamine) and (EtNH₃)₁₀[H₂W₁₂O₄₂]·4H₂O 2 (EtNH₂ = ethylamine). A comparative study reveals a rich structural chemistry of paratungstate. Thermal decomposition of 1 and 2 results in the formation of crystalline monoclinic WO₃.