Structure of the Aqueous Pertechnetate Ion by Raman and Infrared Spectroscopy. Raman and Infrared Spectra of Crystalline KTcO4, KReO4, Na2MoO4, Na2WO4, Na2MoO4·2H2O, and Na2WO4·2H2O

Abstract

The Raman crystal spectra of KTcO4, KReO4, Na2MoO4, Na2WO4, Na2MoO4·2H2O, and Na2WO4·2H2O, and the Raman aqueous spectra of TcO4— and MoO42— have been observed. Infrared spectra of Nujol mulls of all the salts were measured in the rock salt region. Infrared spectra in the CsBr region were also obtained for Na2MoO4 and Na2WO4. For the tetrahedral ions (Td symmetry) of the latter two salts v2(e)>v4(f2), which represents an inversion of the usual order. Examination of all the spectra leads to the conclusion that the Raman spectrum of aqueous pertechnetate ion, which shows only two lines, represents the spectrum of tetrahedral TcO4— ion perturbed by the close association of water molecules. The appearance of two instead of four Raman lines in the spectrum is shown to result from the accidental degeneracy of v1(a1) and v3(f2) vibrations. The v2(e) line is not detected probably because of its low intensity and broadness. The observation of three rather than the expected four Raman lines for molybdate ion is similarly believed to be due to the low intensity and broadness of the v2(e) line. This explanation is also offered as an alternative explanation for the absence of the fourth line in the Raman spectrum of ReO4—(aq) and WO42—(aq) to that previously given, namely, that v2(e) and v4(f2) are sufficiently close together that they are unresolved.