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

Abstract

Three new phenyltin-substituted polyoxometalates, ((CH₃)₂NH₂)₄[Sn(C₆H₅)PW₁₁O₃₉] (1), K₇[Sn(C₆H₅)P₂W₁₇O₆₁] (2), and ((CH₃)₂NH₂)₆K[Sn(C₆H₅)(H₂O)P₂W₂₀O₇₀(H₂O)₂] (3), have been synthesized and characterized by single crystal X-ray diffraction, ³¹P and ¹H 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–π 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 mono-substituted polyoxometalates, an attribute that usually renders structural and structure-related reactivity studies of this large class of polyoxometalates quite difficult.