Mixed-valent vanadium substituted polyoxometalates: the wheel shaped [Rb3⊂{VVVIV3O7(H2O)6}2{H6P6W39O147(H2O)3}]15−We wish to dedicate this paper to Prof. Michael T. Pope on the occasion of this 77th birthday.Electronic Supplementary Information (ESI) available: Details of crystallographic studies, thermogram, BVS calculations, 31P NMR and IR spectra for 1a. See DOI: 10.1039/c0ce00068j

The wheel shaped polyoxoanion [Rb 3 ⊂ {V V V IV 3 O 7 (H 2 O) 6 } 2 {H 6 P 6 W 39 O 147 (H 2 O) 3 }] 15− comprising a macrocyclic tungstophosphate template wheel [P 6 W 39 O 147 (H 2 O) 3 ] 30− ({P 6 W 39 }) capped by two unprecedented mixed-valent oxovanadium {(V V &z.dbd;O)(V IV &z.dbd;O) 3 (µ 2 -O) 3 (H 2 O) 6 } 3+ groups has been prepared and characterized by X-ray diffraction, elemental analysis, TGA, IR and 31 P NMR spectroscopy. The title polyanion represents the first example of the {P 6 W 39 } unit stabilizing a polynuclear metal assembly. A wheel shaped 39-tungsto-6-phosphate {P 6 W 39 } macrocycle has been prepared which stabilizes two unprecedent mixed-valent vanadium units {(V V &z.dbd;O)(V IV &z.dbd;O) 3 (µ 2 -O) 3 (H 2 O) 6 } 3+ .