Synthesis of Polyoxovanadates from Aqueous Solutions

摘要

Polyoxovanadates have been synthesized from aqueous solutions of V~V in presence of inorganic Na~+ and organic [N(CH_3)_4]~+ cations . Decavanadate crystals are precitiptated at room temperature around pH 7, whereas layered compounds Na[V_3O_8].H_2O and N(CH_3)_4[V_4O(10)] are formed at the same pH under hydrothermal conditions .In situ ~(51)V NMR experiments show that upon heating solute decavanadate species are propressively transformed into cyclic metavanadates [V_4O_(12)]~(4-).A chemical mechanism of suggested for the formation of these layered vanadium oxides . It involves the ring-opening polymerization of cyclic metavanadates arising from co-ordination expansion favored by protonation or vanadium reduction