Two New Polyoxovanadate-supported Transition Metal Complexes: [Zn(en)2][Zn(en)2(H2O)2][{Zn(en)(enMe)}As6V15O42(H2O)]·4H2O and [Zn2(enMe)2(en)3][{Zn(enMe)2}As6V15O42(H2O)]·4H2O

Composition-driven archetype dynamics in polyoxovanadates

Molecular metal oxides often adopt common structural frameworks (i.e. archetypes), many of them boasting impressive structural robustness and stability. However, the ability to adapt and to undergo transformations between different structural archetypes is a desirable material design feature offering applicability in different environments. Using systems thinking approach that integrates synthetic, analytical and computational techniques, we explore the transformations governing the chemistry of polyoxovanadates (POVs) constructed of arsenate and vanadate building units. The water-soluble salt of the low nuclearity polyanion [V₆As₈O₂₆]⁴⁻ can be effectively used for the synthesis of the larger spherical (i.e. kegginoidal) mixed-valent [V₁₂As₈O₄₀]⁴⁻ precipitate, while the novel [V₁₀As₁₂O₄₀]⁸⁻ POVs having tubular cyclic structures are another, well soluble product. Surprisingly, in contrast to the common observation that high-nuclearity polyoxometalate (POM) clusters are fragmented to form smaller moieties in solution, the low nuclearity [V₆As₈O₂₆]⁴⁻ anion is in situ transformed into the higher nuclearity cluster anions. The obtained products support a conceptually new model that is outlined in this article and that describes a continuous evolution between spherical and cyclic POV assemblies. This new model represents a milestone on the way to rational and designable POV self-assemblies.

Systems-based elucidation of the polyoxovanadate speciation reveals that heterogroup substitution can transform spherical kegginoids into tubular architectures in a programmable manner.

Semimetal-functionalised polyoxovanadates

Polyoxovanadates (POVs), known for their wide applicability and relevance in chemical, physical and biological sciences, are a subclass of polyoxometalates and usually self-assemble in aqueous-phase, pH-controlled condensation reactions. Archetypical POVs such as the robust [VO42](12-) polyoxoanion can be structurally, electronically and magnetically altered by heavier group 14 and 15 elements to afford Si-, Ge-, As- or Sb-decorated POV structures (heteroPOVs). These main-group semimetals introduce specific chemically engineered functionalities which cause the generally hydrophilic heteroPOV compounds to exhibit interesting reactivity towards organic molecules, late transition metal and lanthanoid ions. The fully-oxidised (V(V)), mixed-valent (V(V)/V(IV) and V(IV)/V(III)), "fully-reduced" (V(IV)) and "highly-reduced" (V(III)) heteroPOVs possess a number of intriguing properties, ranging from catalytic to molecular magnet characteristics. Herein, we review key developments in the synthetic and structural chemistry as well as the reactivity of POVs functionalised with Si-, Ge-, As- or Sb-based heterogroups.