Hydrothermal routes to new sodium hydrogen polytungstates

The new acidic sodium polytungstates, Na[HW O]·20HO (1) and Na [HWO]·20H O (2), have been synthesised under hydrothermal conditions where variations of pH and temperature allow control of the protonation of the [W O] cluster in the products. The polytungstate cluster, [HWO] , in each compound consists of the well known polyhedral unit based on 12 edge- and corner-sharing WO octahedra, though the decoration of this unit with varying levels of protons results in significant changes in the W-O distances. The polytungstate clusters exist in arrays separated by sodium ions and water molecules forming well separated, (polytungstate centre to centre distance of 10.87 Å), rhombohedrally stacked units in 1 and strongly hydrogen bonded and more tightly packed units, (centre to centre distance of 9.34 Å), due to the high H: Na ratio in 2.