Synthesis\nof Hollowed Polyoxometalate with a Flipped\nVO<sub>5</sub> Unit by the Elimination of a Centered Organic Molecule

Mechanistic understanding of the formation of clusters\nplays a\nrole in designing the structure-dependent properties. Based on the\nfact that anions act as templates to form spherical polyoxovanadates,\nvarious structures were reported by changing anions in the synthetic\nsolution. In this work, another factor in the formation of spherical\npolyoxometalates was demonstrated. By the reaction of [V<sub>10</sub>O<sub>26</sub>]<sup>4–</sup> in acetonitrile with a reductant\nto increase the number of tetravalent V<sup>4+</sup> and <i>p</i>-toluene sulfonic acid to convert tetrahedral VO<sub>4</sub> units\nto square-pyramidal VO<sub>5</sub>, acetonitrile-containing polyoxovanadate\n[V<sub>24</sub>O<sub>60</sub>(CH<sub>3</sub>CN)]<sup>6–</sup> (<b>I</b><sup><b>CH3CN</b></sup>) was synthesized. The\nbulky and hydrophobic aromatic rings prevented the formed anions from\nacting as a template. By changing the synthetic solvent, encapsulated\nmoieties were controlled. Nitromethane was also encapsulated to afford\n[V<sub>24</sub>O<sub>60</sub>(CH<sub>3</sub>NO<sub>2</sub>)]<sup>6–</sup> (<b>I</b><sup><b>CH3NO2</b></sup>). When acetone was\nused as the solvent, the contaminated water was encapsulated to form\n[V<sub>24</sub>O<sub>60</sub>(H<sub>2</sub>O)]<sup>6–</sup> (<b>I</b><sup><b>H2O</b></sup>). The encapsulated acetonitrile\nmolecule was eliminated by heating <b>I</b><sup><b>CH3CN</b></sup> up to 230 °C under N<sub>2</sub> flow conditions to give\nhollowed polyoxovanadate [V<sub>24</sub>O<sub>60</sub>]<sup>6–</sup> (<b>II</b>), even though <b>I</b><sup><b>CH3CN</b></sup> possesses no pores for acetonitrile to pass. From the X-ray\ncrystallographic analysis of <b>II</b>, one of the 24 VO<sub>5</sub> units was flipped. The electrochemical properties and catalytic\nperformances between <b>I</b><sup><b>CH3CN</b></sup> and <b>II</b> were also investigated.