Transition Metals Oxoanions and Polynuclear Species

Transition Metals Oxoanions and Polynuclear Species.—References in this section will be dealt with in an order dictated partly by increasing complexity of the oxoanion and partly by Periodic Table position. 

The half-life for exchange of 0 with [VOi] - at 273 K in basic aqueous solution is a few seconds. The rate is first-order in [V04] and almost independent of hy- 

Tanaka, and T. Tanaka, fnorg. Chim. Acta, 1977, 21, 229. 

Rates of decomposition of the phosphododecavanadate ion [H4PVi2036] depend on the concentration of acid or of alkali present. The vanadium is stated to end up in the form of [VO2] in acid solution, [HV04] and [HV207] in alka-line. Vanadium(v) is known to catalyse hydrolysis of polyphosphates. The maximum catalytic effect corresponds to the participation of a [V2P30io] anion (or some appropriately protonated form thereof), whose enthalpy of activation for dissociation must be unusually low.  

Difficulties of characterizing intermediates and products make mechanistic conjecture on the formation of polyniobates difficult. However, the intermediacy of [NbsOig] - entities has been suggested in the building up of polynuclear species of molecular weights of the order of a thousand or more.  

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