Hydrophobic interaction of V12 bowl-type dodecavanadates with alkyl ammonium cations

Synthesis of Hollowed Polyoxometalate with a Flipped VO5 Unit by the Elimination of a Centered Organic Molecule

Mechanistic understanding of the formation of clusters plays a role in designing the structure-dependent properties. Based on the fact that anions act as templates to form spherical polyoxovanadates, various structures were reported by changing anions in the synthetic solution. In this work, another factor in the formation of spherical polyoxometalates was demonstrated. By the reaction of [V10O26]4- in acetonitrile with a reductant to increase the number of tetravalent V4+ and p-toluene sulfonic acid to convert tetrahedral VO4 units to square-pyramidal VO5, acetonitrile-containing polyoxovanadate [V24O60(CH3CN)]6- (ICH3CN) was synthesized. The bulky and hydrophobic aromatic rings prevented the formed anions from acting as a template. By changing the synthetic solvent, encapsulated moieties were controlled. Nitromethane was also encapsulated to afford [V24O60(CH3NO2)]6- (ICH3NO2). When acetone was used as the solvent, the contaminated water was encapsulated to form [V24O60(H2O)]6- (IH2O). The encapsulated acetonitrile molecule was eliminated by heating ICH3CN up to 230 °C under N2 flow conditions to give hollowed polyoxovanadate [V24O60]6- (II), even though ICH3CN possesses no pores for acetonitrile to pass. From the X-ray crystallographic analysis of II, one of the 24 VO5 units was flipped. The electrochemical properties and catalytic performances between ICH3CN and II were also investigated.

Mechanistic insights into template-driven polyoxovanadate self-assembly: the role of internal and external templates

The self-assembly of molecular metal oxides, polyoxometalates (POMs), can be controlled using internal or, more rarely, external templates. Here, we explore how the interplay between internal templates (halides, oxoanions) and organic external templates (protonated cyclene species) affect the self-assembly of a model polyoxovanadate cluster, [V₁₂O₃₂X]^n- (X = Cl^-, Br^-, NO₃^-). A combination of crystallographic analyses, spectroscopic studies and in situ as well as solid-state ⁵¹V NMR spectroscopy provide critical insights into the initial formation of an intermediate vanadate species formed during the process. Structural and spectroscopic studies suggest that a direct interaction between internal and external templates allows tuning of the internal template position within the cluster cavity. These insights form the basis for further developing the template-driven synthetic chemistry of polyoxovanadates.