Cyclic Ti₉ Keggin Trimers with Tetrahedral (PO₄) or Octahedral (TiO₆) Capping Groups

We have synthesized the cyclic Ti9 Keggin trimers [(α-Ti3PW9O38)3(PO4)]18− (1) and [(α-Ti3SiW9O37OH)3(TiO3(OH2)3)]17− (2), which are both composed of three (Ti3XW9O37) units (X = P or Si) linked via three Ti−O−Ti bridges and a capping group, which is either tetrahedral PO4 (1) or octahedral TiO6 (2). Polyanions 1 and 2 were fully characterized in the solid state (IR, X-ray diffraction, thermogravimetric and elemental analyses) and in solution (31P or 183W NMR).