Mono-substituted Keggin, Wells-Dawson and {P2W21}-type polyoxometalates without positional disorder

Three new phenyltin-substituted polyoxometalates, ((CH3)(2)NH2)(4)[Sn(C6H5)PW11O39] (1), K-7[Sn(C6H5)P2W17O61] (2), and ((CH3)(2)NH2)(6)K[Sn(C6H5)(H2O)P2W20O70(H2O)(2)] (3), have been synthesized and characterized by single crystal X-ray diffraction, P-31 and H-1 NMR, and FT-IR spectroscopy. Significantly, the mono-substituted phenyltin group in all three complexes is not positionally disordered. The Sn(C6H5) group is unambiguously determined and refined anisotropically with full occupancy, a result that is very unusual for mono-substituted polyoxometalates, and in particular polytungstates. Three factors account for these disorder-free mono-phenyltin-substituted polyanion structures: the steric bulk and rigidity of the phenyl group, hydrogen bonding and cation-pi interactions between the phenyl ring and countercations. These results demonstrate the ability of a phenyl group to remove the crystallographically imposed positional disorder typically seen in monosubstituted polyoxometalates, an attribute that usually renders structural and structure-related reactivity studies of this large class of polyoxometalates quite difficult.