Hexalacunary [α‐H2P2W12O48]12− Wells‐Dawson Anion: X‐ray Crystal Structural Evidence and Oligomerization to WO(OH2)4+‐Bridged Dimer and Trimers

Abstract

AbstractWe report the first single‐crystal X‐ray structural evidence of the potassium salt of the hexalacunary [α‐H2P2W12O48]12− (abbreviated as {P2W12}) anion after its discovery by Contant and Ciabrini in 1977. In addition, we observed oligomerization of {P2W12} into a {WO(OH2)}4+‐bridged Pacman‐shaped [{WO(OH2)}(α‐HP2W12O48)2]22− ({P4W25}) dimer and a cyclic [{WO(OH2)}3(P2W12O48)3]30− ({P6W39}) trimer. The three phosphotungstate anions were synthesized through recrystallization of (NH4)12[α‐H2P2W12O48] from slightly alkaline (HOCH2)3CNH2/KCl, CH3NH3Cl/KCl, and CH3NH3Cl/NH4Cl solutions. The structure of {P2W12} is derived from [α‐P2W18O62]6− that has six tungsten atoms one from each polar group and four from the belt–removed, and the center of the lacunary site is capped by a potassium cation. Structures of {P4W25} and {P6W39} are constructed by connecting two and three {P2W12} units with {WO(OH2)}4+, respectively. The isolation of a pure {P6W39} phosphotungstate framework without coordination with transition metal cations is unprecedented. Powder X‐ray diffraction confirmed the bulk purity of these compounds, indicating that selective crystallization was achieved through the selection of countercations and pH.