AQUEOUS MOLYBDOTUNGSTATES

Molybdenum(VI) has been shown by W-183 NMR spectroscopy to replace W(V I) in the three main types of aqueous polytungstate anion. In ions wit h the paratungstate-A structure, [W7O24]6- it can replace any or all o f the tungstens, so that at least 19 mixed-metal species can be observ ed, and mostly also identified. Their relative stability constants can also be approximately determined using the LAKE program. The proporti ons of these species can be semiquantitatively explained by a simple s ite-preference model, and their chemical shifts are largely governed b y the overall extent of substitution. In contrast, only a single molyb denum substitution was observed in alpha-metatungstate, alpha-[H2W12O4 0]6-, and also in paratungstate-B, [H2W12O42]10- at the site furthest from the centre of the anion.