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

Abstract

An attempted isolation of the elusive diammonium tetraoxidotungstate (NH sub(4)) sub(2)[WO sub(4)] as its imidazole (Im) adduct resulted in the serendipitous formation of hepta(ammonium) penta(1H-imidazol-3-ium) paratungstate B tetrahydrate having formula [NH sub(4)] sub(7)[ImH] sub(5)[W sub(12)O sub(42)].4H sub(2)O (1). The synthesis, vibrational spectra, crystal structure and thermal study of the mixed cationic paratungstate tetrahydrate 1 are reported. The structure of 1 consists of a centrosymmetric paratungstate [W sub(12)O sub(42)] sup(12-) anion devoid of internal hydrogen atoms, which is charge balanced by ammonium and 1H-imidazol-3-ium cations. One of the four unique NH sub(4)+ cations and one of the three crystallographically independent 1H-imidazol-3-ium cations are disordered around a center of inversion. The cations, [W sub(12)O sub(42)] sup(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 1 results in the formation of monoclinic tungsten trioxide WO sub(3).