Tetrakis(dimethyltin)-Containing Tungstophosphate [{Sn(CH3)2}4(H2P4W24O92)2]28-: First Evidence for a Lacunary Preyssler Ion

We demonstrate for the first time that the superlacunary polyanion [H2P4W24O94]22- reacts with electrophiles. One-pot reaction of this precursor polyanion with dimethyltin dichloride in aqueous acidic medium results in the hybrid organic−inorganic [{Sn(CH3)2}4(H2P4W24O92)2]28- (1). Single-crystal X-ray analysis was carried out on K17Li11[{Sn(CH3)2}4(H2P4W24O92)2]·51H2O (1a), which crystallizes in the tetragonal system, space group P42/nmc, a = b = 21.5112(17) and c = 27.171(3) Å, and Z = 2. Polyanion 1 is composed of two (P4W24O92) fragments that are linked by four equivalent diorganotin groups. The unprecedented assembly 1 has D2d symmetry and contains a hydrophobic pocket in the center of the molecule. The cyclic voltammetry pattern of 1 is constituted by a first broad, 16-electron reduction wave followed by a second large current intensity wave. No splitting of the first reduction wave could be obtained at moderate scan rate values, even though two well-separated oxidation processes are associated with it. The characteristics of the first wave are clearly different from those obtained for the polyanion precursor [H2P4W24O94]22- and the related, wheel-shaped [H7P8W48O184]33-, which is due to the {Sn(CH3)2} fragments in 1. However, no feature was observed in the voltammogram which could be associated with reduction of the Sn centers.