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)₃Ta(O₂)₄], K₃Ta(O₂)₄], Rb₃Ta(O₂)₄] and Cs₃Ta(O₂)₄] have been prepared and investigated by X-ray powder methods as well as Raman- and IR-spectroscopy. In the case of Rb₃Ta(O₂)₄] the structure has been solved from single crystal data. It is shown that all these compounds are isotypic and crystallize in the K₃Cr(O₂)₄] type (SG , No. 121). The infrared- and Raman spectra (recorded on powdered samples) are discussed with respect to the internal vibrations of the peroxo-group and the dodecahedral Ta(O₂)₄]³⁻ ion. Symmetry coordinates for the Ta(O₂)₄]³⁻ ion are given from which the vibrational modes of the O-O stretching vibrations of the O₂²⁻ groups, the Ta-O stretching vibrations and the Ta-O bending vibrations are deduced.