Hexalacunary [α-H P W O ] Wells-Dawson Anion: X-ray Crystal Structural Evidence and Oligomerization to WO(OH ) -Bridged Dimer and Trimers.

We report the first single-crystal X-ray structural evidence of the potassium salt of the hexalacunary [α-H P W O ] (abbreviated as {P W }) anion after its discovery by Contant and Ciabrini in 1977. In addition, we observed oligomerization of {P W } into a {WO(OH )} -bridged Pacman-shaped [{WO(OH )}(α-HP W O ) ] ({P W }) dimer and a cyclic [{WO(OH )} (P W O ) ] ({P W }) trimer. The three phosphotungstate anions were synthesized through recrystallization of (NH ) [α-H P W O ] from slightly alkaline (HOCH ) CNH /KCl, CH NH Cl/KCl, and CH NH Cl/NH Cl solutions. The structure of {P W } is derived from [α-P W O ] 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 {P W } and {P W } are constructed by connecting two and three {P W } units with {WO(OH )} , respectively. The isolation of a pure {P W } 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.