Synthesis, crystal structure and properties of hepta(ammonium) penta(1H-imidazol-3-ium) paratungstate B tetrahydrate

An attempted isolation of the elusive diammonium tetraoxidotungstate (NH₄)₂[WO₄] as its imidazole (Im) adduct resulted in the serendipitous formation of hepta(ammonium) penta(1H-imidazol-3-ium) paratungstate B tetrahydrate having formula [NH₄]₇[ImH]₅[W₁₂O₄₂]·4H₂O (<b>1</b>). The synthesis, vibrational spectra, crystal structure and thermal study of the mixed cationic paratungstate tetrahydrate <b>1</b> are reported. The structure of <b>1</b> consists of a centrosymmetric paratungstate [W₁₂O₄₂]^12– anion devoid of internal hydrogen atoms, which is charge balanced by ammonium and 1H-imidazol-3-ium cations. One of the four unique NH₄⁺ cations and one of the three crystallographically independent 1H-imidazol-3-ium cations are disordered around a center of inversion. The cations, [W₁₂O₄₂]^12– anion and the unique lattice water molecules are joined with the aid of five varieties of hydrogen bonding interactions. A comparative study of twenty-three partaungstates is described. Thermal decomposition of <b>1</b> results in the formation of monoclinic tungsten trioxide WO₃.