Selenium vibrational frequencies

In earlier work,i 3 Allinger et al. determined MM2 parameters for organoselenium and -tellurium compounds. The selenium parameters were fit to structures and vibrational frequencies of methyl selenol, dimethyl selenide, ethyl selenol, and tetrahydroselenophene. The structures of the tellurium analogs were also calculated, but since only a bond length for Te—C and a bond angle for C-Te-C from dimethyltelluride were known, the authors were unable to compare the results to experimental data. 

Substiiution of one of the Y atoms of a pyramidal XYj molecule by a Z atom lowers the symmetry from Cj to C. Then the degenerate vibrations split into two bands, and all six vibrations become infrared and Raman active. The relationship between C3 and C is shown in Table II-3d. Table ll-3e lists the vibrational frequencies of pyramidal ZXY2 molecules. Simon and Paet-zold made an extensive study of the vibrational spectra of selenium compounds. The ZXYW-type molecule belongs to the C, point group, and all six vibrations are infrared and Raman active. The vibrational spectra of OSClBr and [XSnYZ] (X, Y, Z a halogen) have been reported. 

Raman spectroscopy is a useful probe for detecting transannular S - S interactions in bicyclic or cage S-N molecules or ions. The strongly Raman active vibrations occur at frequencies in the range 180-300 cm-1, and for S- -S distances in the range 2.4-2.7 A. On the basis of symmetry considerations, the Raman spectrum of the mixed sulfur-selenium nitride S2Se2N4 was assigned to the 1,5- rather than the 1,3- isomer.37... 

Patel et al. °"> successfully operated parametric oscillators in the infrared region (2.5 - 25 pm) using the nonlinear characteristics of tellurium and selenium single crystals. This frequency range is important for the molecular spectroscopy of rotational-vibrational... 

Compounds of sulfur and selenium are of great interest for spectroscopists because of their unusual structures and strong Raman bands involving S—S or Se—Se bonds. Steudel and co-workers have made an extensive study on vibrational spectra of these compounds. Figure 2.76 shows a group frequency chart for sulfur compounds. 

As expected, when comparing vibrational spectra of sulfur and selenium compounds, the absorptions due to bonds to selenium occur at lower frequencies than the corresponding sulfur modes. This frequency shift is normally 50-150 cm" but may be more for selenium-oxygen compounds when compared to sulfur-oxygen compounds ... 

The vibrational spectra of (a) selenium tetrafluoride in the vapour and solid phases, and isolated in inert-gas matrices, and (6) tellurium tetrafluoride, in both the solid and matrix-isolated condition, have been reported. The fundamental frequencies were assigned on the basis of the symmetry of discrete SeF4 and Tep4 molecules force constants, obtained by normal-coordinate analysis, showed that the axial bonds are weaker than the equatorial... 

For metal complexes in which the metal ion is directly bound to the selenium atom, the former band position tends to higher frequencies whilst the latter tends to lower frequencies. Selenoamides have a medium-intensity band at 1200-1000cm (8.33-10.00pm) which also has a contribution from the C=Se bond vibration. The spectra of other compounds with the N-C=Se group are similar to those of selenoamides. 

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