Synthesis, spectral and structural characterization of organic ammonium paratungstates

Abstract

Dissolution of tungsten(VI) oxide hydrate (WO₃·H₂O) in aqueous organic amine (RNH₂ where R = methyl or ethyl, or <em>n</em>-propyl or isopropyl or <em>n</em>-butyl or <em>t</em>-butyl etc.) results in the formation of the tetrahedral tetraoxidotungstate(VI) species in solution. Slow evaporation of the reaction mixture to isolate the 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 paper, we report on the synthesis, Raman spectra, crystal structures and properties of two organic ammonium paratungstates <em>viz</em>. (MeNH₃)₁₀[H₂W₁₂O₄₂]·12H₂O <strong>1</strong> (MeNH₂ = methylamine) and (EtNH₃)₁₀[H₂W₁₂O₄₂]·4H₂O <strong>2 (</strong>EtNH₂ = ethylamine). Thermal decomposition of <strong>1</strong> or <strong>2</strong> at 800 °C results in the formation of monoclinic form of tungsten trioxide WO₃. A comparative study of several paratungstates is described.