Cyclic Ti9 keggin trimers with tetrahedral (PO4) or octahedral (TiO6) capping groups

We have synthesized the cyclic Ti 9 Keggin trimers (alpha-Ti 3PW 9O 38) 3(PO 4)] (18-) ( 1) and (alpha-Ti 3SiW 9O 37OH) 3(TiO 3(OH 2) 3)] (17-) ( 2), which are both composed of three (Ti 3XW 9O 37) units (X = P or Si) linked via three Ti-O-Ti bridges and a capping group, which is either tetrahedral PO 4 ( 1) or octahedral TiO 6 ( 2). Polyanions 1 and 2 were fully characterized in the solid state (IR, X-ray diffraction, thermogravimetric and elemental analyses) and in solution ( (31)P or (183)W NMR).