Does an all-sulphur analogue of heptamolybdate exist?

Abstract

The complexes [MoX4](2-) (M = Mo; X = O or S) exist as the monomeric tetrahedral species in aqueous alkaline solutions. Acidification of tetraoxomolybdate results in the condensation of the tetrahedral units via a series of polyoxomolybdates leading to the ultimate formation of the trioxide MoO3. Heptamolybdate [Mo7O24](6-) is the first major polyanion of the acidification reaction.In contrast, acidification of tetrathiomolybdates leads to the formation of amorphous molybdenum trisulphide via a dinuclear Mo(V) complex. The formation of the dinuclear Mo(V) complex precludes the formation of any higher nuclearity Mo(VI)-S complexes in aqueous solution. Thus it is shown that the all-sulphur analogue of heptamolybdate [Mo7S24](6-) does not exist in alkaline medium and also cannot be isolated from aqueous acidic medium.