The antimony(III)-bridged heteropolyanion sandwich dimers [SbIII3(A-α-XW9O34)2]11- (X = SiIV, GeIV) and C-shaped double-sandwich [SbIII6O2(PW6O26)(A-α-PW9O34)2]15-

Interaction of potassium antimony(III) tartrate hydrate K-2(SbC4H2O6)(2)center dot 3H(2)O with the trilacunary Keggin derivatives [A-alpha-XW9O34](10-) (X = Si-IV, Ge-IV) and [A-alpha-PW9O34](9-) in aqueous acidic medium (pH 4.8) resulted in three novel polyanions, [Sb-3(A-alpha-XW9O34)(2)](11-) (X = Si-IV (1), Ge-IV (2)) and [Sb6O2(A-PW6O26)(A-alpha-PW9O34)(2)](15-) (3), which were isolated as the hydrated potassium salts K-11[Sb-3(A-alpha-XW9O34)(2)]center dot 31H(2)O (X = Si-IV (K-1), Ge-IV (K-2)) and the mixed potassium-sodium salt K14Na[Sb6O2(A-PW6O26)(A-alpha-PW9O34)(2)]center dot 61H(2)O (KNa-3) salts, respectively, and characterized by single-crystal X-ray diffraction, IR spectroscopy, as well as elemental and thermogravimetric analyses. The Sb-III-containing polyanions 1-3 possess unique structural features, as they represent the first examples of sandwich-type POMs with trigonal-pyramidal (SbO3)-O-III linkers. The stability of 1-3 in aqueous media was investigated by multinuclear (W-183, P-31) NMR and UV-Vis spectroscopy.