Bonding Insights From Structural And Spectroscopic Comparisons Of {Snw5} And {Tiw5} Alkoxido- And Aryloxido-Substituted Lindqvist Polyoxometalates

Incorporation of {MX}(n+) groups into polyoxometalates (POMs) provides the means not only to introduce reactivity and functionality but also to tune the electronic properties of the oxide framework by varying M, X and n. In order to elucidate the factors responsible for differences in reactivity between {TiW5} and {SnW5} Lindqvist-type hexametalates, a series of alkoxido- and aryloxido-tin substituted POMs (nBu(4)N)(3)[(RO)SnW5O18] (R=Me, Et, iPr and tBu) and (nBu(4)N)(3)[(ArO)SnW5O18] (Ar=C6H5, 4-MeC6H5, 4-tBuC(6)H(5), 4-HOC6H4, 3-HOC6H4 and 2-CHOC6H4) has been structurally characterised and studied by multinuclear NMR (H-1, C-13, O-17, Sn-119 and W-183) and FTIR spectroscopy. Spectroscopic and structural parameters were compared with those of titanium-substituted homologues and, when coupled with theoretical studies, indicated that Sn-OR and Sn-OAr bonds are ionic with little -contribution, whereas Ti-OR and Ti-OAr bonds are more covalent with -bonding that is more prevalent for Ti-OR than Ti-OAr. This experimental and theoretical analysis of bonding in a homologous series of reactive POMs is the most extensive and detailed to date, and reveals factors which account for significant differences in reactivity between tin and titanium congeners.