CO3]13 (M = Y3+ and Yb3+) have been synthesized at room temperature by stoichiometric reactions of the trilacunary A-b-SiW9O34 10 ligand with M3+ in 0.1 M carbonate solution. The new complexes were isolated as sodium and mixed sodium/potassium salts and were characterized by elemental analysis, IR, 13C and 29Si NMR, UV–Vis spectroscopy, TGA, DSC and single crystal structure analysis. The crystal structure of the complexes consist of two lacunary A-b-SiW9O34 10 Keggin moieties which are linked by a (H2OMO)3C belt into an assembly of virtual C2 symmetry. Each M3+ ion adopts a mono-capped trigonal- prismatic coordination. The C2 axis of the complexes and the local 3-fold axis of the MO6 group lies in the (H2OMO)3C belt plane. The trigonal prismatic geometry is achieved by the two terminal oxygen atoms of an edge shared pair of WO6 octahedra from each A-b-SiW9O34 10 moiety and two oxygen from the belt, and the cap by one external water ligand. The hydrolytic and thermal stabilities of the complexes and the reasons that prove the retention of the isomeric form of the trilacunary A-b-SiW9O34 10 ligand upon complexation are discussed.
