Cyclic [Ti.sub.9] Keggin trimers with tetrahedral (P[O.sub.4]) or octahedral (Ti[O.sub.6]) capping groups

The synthesis and structural characterization of the two polyanions, [[([alpha]-[Ti.sub.3]P[W.sub.9][O.sub.38]).sub.3](P[O.sub.4])](18-) and [[([alpha]-[Ti.sub.3]Si[W.sub.9][O.sub.37]OH).sub.3](Ti[O.sub.3][([OH.sub.2]).sub.3])](17-) as the first examples of trimeric Ti-containing polytungstates are reported. Both the complexes are composed of three ([Ti.sub.3]X[W.sub.9][O.sub.37]) units (X = P or Si) linked via three Ti-O-Ti bridges and a capping group, which is either tetrahedral P[O.sub.4] or octahedral Ti[O.sub.6].