6-peroxo-6-zirconium crown and its hafnium analogue embedded in a. triangular polyanion:: [M6(O2)6(OH)6(γ-SiW10O36)3]18 (M = zr, hf)

We have synthesized and structurally characterized the unprecedented peroxo-zirconium(IV) containing [Zr(6)(O(2))(6)(OH)(6)(gamma-SiW(10)O(36))(3)](18-) (1). Polyanion 1 comprises a cyclic 6 -peroxo-6-zirconium core stabilized by three decatungstosilicate units. We have also prepared the isostructural hafnium(V). analogue [Hf(6)(O)(6)(OH)(6)(gamma-SiW(10)O(36))(3)](18-) (2). We investigated the acid/base and redox properties of 1 by UV-vis spectroscopy and electrochemistry studies. Polyanion 1 represents the first structurally characterized Zr-peroxo POM with side-on, bridging peroxo units. The simple, one-pot synthesis of 1 and 2 involving dropwise addition of aqueous hydrogen peroxide could represent a general procedure for incorporating peroxo groups into a large variety of transition metal and lanthanide containing POMs.