Vibrational spectroscopy of some organometallic complexes.

The vibrational spectra of some metal carbonyl and organometallic complexes are reported and assigned. Emphasis is placed upon Raman data and the instrumentation and sampling techniques of laser Raman spectroscopy are discussed. Oriented single crystal Raman spectra are presented for M2(CO)10 M = Mn, Re, together with new solution data. These allow a reassignment of the vibrational spectra of these molecules. The spectra of M(CO)3(?-Arene) complexes are considered, M = Cr, Mo, W, or Mn; arene = benzene, aniline, anisole, methylbenzoate, toluene, mesitylene, hexamethylbenzene, cyclopentadiene or methylcyclopentadiene. The spectra of the free and co-ordinated ligands are compared, and the ro1e of charge back-donation from the metal atom to the ring is considered, qualitatively. An attempt is made to relate the magnitude of the back-donation to the frequency shifts of the internal vibrations of the arene upon co-ordination. Intense Raman bands at ~100 cm-1 are found to be characteristic of many metal carbonyl complexes. The nature of these bands is considered. Frequencies and assignments of the vibrational spectra of palladium ?-allyl and ?-2-methylallyl halogen dimers are presented. The possible structural change in solution is considered. All solid-state spectra are considered in terms of a factor group analysis, where appropriate crystal structure data are available. It is shown that point molecular symmetry is usually a poor approximation when interpreting solid-state spectra. The concept of 'local symmetry' is discussed critically, and also shown to be an inadequate approximation, except for some non-axially symmetric systems.