Titanium-Substituted Polyoxotantalate Clusters Exhibiting Wide pH Stabilities: [Ti2Ta8O28]8- and [Ti12Ta6O44]10-

Two new substituted polyoxotantalate clusters, [Ti2Ta8O28](8-) and [Ti12Ta6O44](10-), considerably expand the pH range where tantalates persist in aqueous solution. The structures of [Ti2Ta8O28](8-) and [Ti12Ta6O44](10-) are reported as tetramethylammonium salts after synthesis at hydrothermal conditions in aqueous solution. These Ti-substituted polyoxotantalate clusters have analogues among recently discovered niobates, but are slightly larger and more persistent in solution. Most importantly, they exhibit a much wider range of pH stability than the familiar hexatantalate cluster, which is the only other tantalate known to be stable at highly basic pH conditions. These molecules are kinetically stable to near-neutral pH, making them excellent synthons for further development into materials and catalysts, and an significant advance in adapting tantalates for use in aqueous solutions.