Vibrational spectra of the peroxotantalates (NH4)3[Ta(O2)4], K3[Ta(O2)4], Rb3[Ta(O2)4] and CS3[Ta(O2)4] and the crystal structure of Rb3[Ta(O2)4]

The compounds (NH4)(3)[Ta(O-2)(4)], K-3[Ta(O-2)(4)], Rb-3[Ta(O-2)(4)] and Cs-3[Ta(O-2)(4)] have been prepared and investigated by X-ray powder methods as well as Raman- and IR-spectroscopy. In the case of Rb-3[Ta(O-2)(4)] the structure has been solved from single crystal data. It is shown that all these compounds are isotypic and crystallize in the K-3[Cr(O-2)(4)] type (SG I (4) over bar 2m, No. 121). The infrared- and Raman spectra (recorded on powdered samples) are discussed with respect to the internal vibrations of the peroxogroup and the dodecahedral [Ta(O-2)(4)](3-) ion. Symmetry coordinates for the [Ta(O-2)(4)](3-) ion are given from which the vibrational modes of the O-O stretching vibrations of the O-2(2-) groups, the Ta-O stretching vibrations and the Ta-O bending vibrations are deduced. (C) 2004 Elsevier Inc. All rights reserved.