The powder-infrared spectra of different crystalline compounds containing the tetrahedral Cro3-4, anion have been recorded and analyzed with the aid of the site symmetry rules. In some cases Raman data are also reported. The effect of the different crystalline environments is discussed in detail and comparisons with isostructural phases are also made. A definitive assignment for the internal vibrations of the CrO3-4, ion is proposed and a new set of force constants has been calculated fron a modified valence force field.