Structural investigations of sandwich-type heteropolyoxometalate with dinuclear vanadium cluster

The sandwich-type K10[(VO)2Sb2W20O70].20H2O heteropolyoxotungstate was investigated by means of elemental analyses, thermogravimetric and spectroscopic (FT-IR, UV-vis and EPR) methods. The stretching vibration of the terminal W=Ot bonds is shifted with 8 cm-1 towards higher wave numbers in the FT-IR spectrum of the complex, which indicates the involvement of the terminal oxygen atoms in the coordination to the vanadium ions. The UV electronic spectra of the ligand and complex spectrum presents two bands assigned to ligand to metal charge transfer pπ→dπ transitions in the W=Ot bonds and the electron transition dπ→pπ→dπ between the energetic levels of the tricentric bonds W-Ob-W. The powder EPR spectrum obtained at room temperature is typical for mononuclear oxovanadium species in an axial environment. The spectrum exhibits eight components, both in perpendicular and parallel bands due to the hyperfine coupling of the spin of one unpaired electron with the nuclear spin of the 51V isotope (gperpendicular = 1.908, gII = 1.974, Aperpendicular = 69 G, AII = 201 G).