Abstract
The isolation and structural characterisation of a novel tris[peroxotitanium(IV)]‐substituted α‐Dawson polyoxometalate (POM), [α‐1,2,3‐P~2~W~15~(TiO~2~)~3~O~56~(OH)~3~]^9−^ (1a), containing side‐on coordination (i.e. η^2^‐coordination) of the peroxo group to the titanium(IV) atom are described. A water‐soluble, completely inorganic compound of the monomeric POM Na~9~[α‐1,2,3‐P~2~W~15~(TiO~2~)~3~O~56~(OH)~3~]·16H~2~O (1), obtained as analytically pure, homogeneous orange crystals, was obtained from a reaction in aqueous solution of an excess of 30% aqueous hydrogen peroxide with {[α‐1,2,3‐P~2~W~15~Ti~3~O~59~(OH)~3~]~4~[μ~3~‐Ti(OH)~3~]~4~Cl}^33−^ (2a). The latter has been recently shown to be a giant ”tetrapod”‐shaped, tetrameric anhydride formed from the tris[titanium(IV)]‐substituted Dawson substructures with four bridging Ti octahedral groups. Compound 1 could not be obtained from the reaction with another giant tetrapod POM, {[α‐1,2,3‐P~2~W~15~Ti~3~O~57.5~(OH)~3~]~4~Cl}^25−^ (3a), which does not contain the bridging octahedral Ti groups. The molecular structure of 1a was successfully determined by a single‐crystal X‐ray diffraction study and was shown to be a monomeric α‐Dawson POM derived from the tris[peroxotitanium(IV)] species. Bond valence sum (BVS) calculations suggest that the μ~2~‐oxo sites of the three Ti−O−Ti bridges in the Ti~3~ cap of the Dawson unit are protonated. Characterisation of 1 was also accomplished by complete elemental analysis, TG/DTA, FTIR and solution (^31^P and ^183^W) NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)