Long Hydrogen-Bonded Rod of Molecular Oxide: A Hexatantalate Tetramer

A tetra-<i>n</i>-butylammonium (TBA) salt of [H<sub>4.5</sub>(Ta<sub>6</sub>O<sub>19</sub>)]<sup>3.5–</sup> was synthesized by reacting hydrous tantalum oxide with TBAOH. X-ray structural analysis of TBA<sub>3.5</sub>[H<sub>4.5</sub>(Ta<sub>6</sub>O<sub>19</sub>)]·2THF·5.5H<sub>2</sub>O (THF = tetrahydrofuran) revealed that this compound consists of a hydrogen-bonded, rod-shaped tetramer of hexatantalate that is almost 30 Å long together with TBA cations and solvent molecules of crystallization [<i>a</i> = 20.6354(5) Å, <i>b</i> = 25.5951(7) Å, <i>c</i> = 37.2058(8) Å, α = 77.092(1)°, β = 86.177(1)°, γ = 88.683(1)°, <i>V</i> = 19110.9(8) Å<sup>3</sup>, <i>Z</i> = 8, and space group <i>P</i>1̅]. <sup>1</sup>H NMR spectra showed that this tetrameric structure is maintained in solution.