Chemically controlled condensation of polyoxovanadates

A wide range of polyvanadates can be synthesized from aqueous solutions. Va nadium oxide gels V2O5.nH(2)O are formed around the point of zero charge (p H approximate to 2). They;exhibit a ribbon-like structure. Weak interaction s between these ribbons lead to the formation of mesophases in which vanadi um oxide gels or sols behave as nematic liquid crystals. Organic species ca n be easily intercalated between these oxide ribbons leading to the formati on of hybrid nanocomposites made of alternative layers of organic and inorg anic components. Hybrid materials can also be formed at a higher pH in the presence of large organic ions such as [N(CH3)(4)](+) They exhibit layered structures in which organic cations lie between polyoxovanadate planes. Suc h layered structures are not obtained in the presence of anions such as Cl- or I-. Cluster shell polyvanadates are then formed. They are made of negat ively charged polyvanadate hollow spheres in which the negative anion is en capsulated. In this case the organic cations behave as counter ions for the formation of the hybrid crystalline network.