The antimony(iii)-bridged heteropolyanion sandwich dimers [Sb super(III) sub(3)(A - alpha -XW sub(9)O sub(34)) sub(2)] super(11-) (X = Si super(IV), Ge super(IV)) and C-shaped double-sandwich [Sb super(III) sub(6)O sub(2)(PW sub(6)O sub(26) )(A- alpha -PW sub(9)O sub( 34)) sub(2)] super(15-)

Interaction of potassium antimony(iii) tartrate hydrate K sub(2)(SbC sub(4)H sub(2)O sub(6)) sub(2).3H sub(2)O with the trilacunary Keggin derivatives [A- alpha -XW sub(9)O sub( 34)] super(10-) (X = Si super(IV), Ge super(IV)) and [A- alpha -PW sub(9)O sub( 34)] super(9-) in aqueous acidic medium (pH 4.8) resulted in three novel polyanions, [Sb sub(3)(A- alpha -XW sub(9)O sub(34)) sub(2)] super(11-) (X = Si super(IV) (1), Ge super(IV) (2)) and [Sb sub(6)O sub(2)(A-PW sub(6)O sub(26))(A - alpha -PW sub(9)O sub(34)) sub(2)] super(15-) (3), which were isolated as the hydrated potassium salts K sub(11)[Sb sub(3)(A- alpha -XW sub(9)O sub(34)) sub(2)].31H sub(2)O (X = Si super(IV) (K-1), Ge super(IV) (K-2)) and the mixed potassium-sodium salt K sub(14)Na[Sb sub(6)O sub( 2)(A-PW sub(6)O sub(26))(A- alpha -PW sub(9)O sub(34)) sub(2)].61H sub(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 super(III)-containing polyanions 1-3 possess unique structural features, as they represent the first examples of sandwich-type POMs with trigonal-pyramidal Sb super(III)O sub(3) linkers. The stability of 1-3 in aqueous media was investigated by multinuclear ( super(183)W, super(31)P) NMR and UV-Vis spectroscopy.