AQUEOUS MOLYBDOVANADATES AT HIGH MO-V RATIO

Aqueous molybdovanadates have been studied by V-51 NMR spectroscopy over a wide range of metalion concentrations and temperatures in the range pH 1.4-7, and by potentiometry at 25-degrees-C. The structures of the anions cis-[Mo4V2O19]4-, cis-[HMo4V2O19]3-, [Mo5VO19]3-, [Mo4V5O27]5-, [HMo4V5O27]4- and beta-[Mo7VO26]5- have been further confirmed or determined by parallel O-17 NMR studies. Some Mo-95 NMR data are also presented. Less conclusive evidence is also presented for the solution species alpha-[HMo6V2O26]5-, [Mo4VO17]5- and [HMo8V2O32]5- with a planar structure, and several alpha-Keggin species with central vanadium atoms. There is also tentative evidence for alpha-[HMo7VO26]4-, beta-[H2Mo6V2O26]4- and for species of 'double-heptamolybdate' type. Most of the structures are closely related to the known isopolymolybdates or to decavanadate. The vanadium atoms usually prefer central sites and mutual proximity. Calculations on combined precise electromotive force data and quantitative V-51 NMR data [25-degrees-C, 0.6 mol dm-3 Na(Cl) medium] using the least-squares computer program LAKE have established the formation constants. The chemical speciation is illustrated in distribution diagrams.