Mo=O stretching vibration

The Mo02+ group manifests itself in the infrared and/or Raman spectrum in the form of an intense two-band pattern corresponding to the symmetric and asymmetric Mo—O stretching vibrations. Values for representative complexes are shown in Table 2 which also displays the lowest visible absorption bands for those complexes where these are available. The infrared (or Raman) absorptions are by far the most characteristic feature by which to identify the presence of the MoO + unit. 

Fig. 14 RR intensities of nine skeleton vibrations and the metal-oxo stretch of Mo (tpc)(0), all overlaid on the UV-vis absorption spectrum. The Mo-O stretch is the most enhanced, and the blue shifting of the peak implies CT character in the high-energy portion of the Soret manifold. Reprinted with permission from [176]. Copyright 2009 American Chemical Society...

The infra-red spectrum of Mo(CO)3[P(OCH3)3]3 (VIII) shows three absorption bands at 1993,1919, and 1890 cm-1 in the region in which CO stretching frequencies usually appear. But Cr(CO)3(CNCH)3 (IX) has two absorption bands in the C—O stretch region at 1942 and 1860 cm-1. Octahedral ML3(CO)3 complexes can exist in either the mer or fac isomeric forms (Figure 9.2). Assign the structures of the above two molecules. How many bands would you expect to see in the vibrational Raman spectra of these two molecules, and for which of these bands would the scattered Raman radiation be polarized ... 

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