Ligands vibrational spectra

The vibrational spectrum of a metal complex is one of the most convenient and unambigious methods of characterization. However, it has not been possible to study the interactions of metal ions and biological polymers in this way since the number of vibrational bands from the polymer obscure the metal spectrum. The use of laser techniques for Raman spectroscopy now make it very likely that the Raman spectra of metals in the presence of large amounts of biological material will be measured (34). The intensity of Raman lines from metal-ligand vibrations can be... 

We have reported the first direct observation of the vibrational spectrum of an electronically excited state of a metal complex in solution (40). The excited state observed was the emissive and photochemically active metal-to-ligand charge transfer (MLCT) state of Ru(bpy)g+, the vibrational spectrum of which was acquired by time-resolved resonance Raman (TR ) spectroscopy. This study and others (19,41,42) demonstrates the enormous, virtually unique utility of TR in structural elucidation of electronically excited states in solution. 2+... 

The description of spin states as electronic isomers with different metal-ligand distances requires that their vibrational spectra be a superposition of the spectra of the two separate spin states. The relative contribution of the two states to the observed spectrum will change with temperature as the population of the spin states changes. This has been observed (76, 77, 122, 144, 145). Difficulties occur with the assignment of the metal-ligand vibrational frequencies of particular interest for the analysis of the dynamics of spin state transitions. Some success has been achieved with the use of metal isotopic labeling (82, 151), but there are few reliable assignments. 

Table 2 Comparison of intra-ligand vibrational energies as determined from emission spectra of the main sites of Ir(4,6-dFppy)2(acac) in CH2C12 (T=1.7 K, electronic 0-0 transition I — 0 at 21,025 cm4) and of Pt(4,6-dFppy)(acac) in CH2C12 (7=4.2 K, electronic 0-0 transition II/III — 0 at 21,867 cm4) [107] and in n-octane (7=4.2 K, electronic 0-0 transition II/III —> 0 at 21,461 cm4), respectively (compare Sect. 3.3). Corresponding vibrational energies of the free (4,6-dFppy) ligand, determined from a Raman spectrum (7= 298 K, neat ligand), are also given [53]...

The visible spectrum of this intermediate consists of a band at Amax = 614 nm. Excitation at 614 nm gives resonance Raman enhanced bands at 416 and 666 cm-1 that shift to 408 and 638 cm-1 upon addition of H21sO, indicating exchange with water. These bands are unaffected by the addition of D20. This behavior is consistent with an FeO stretch and the shift observed upon substitution agrees with the expected shift of 29 cm-1. The second peak at 416 cm-1 was attributed to a metal-ligand vibration coupled to the iron-oxo stretch. 

A number of (substituted borazine)chromium tricarbonyl complexes have been prepared. 0 The chief change in the vibrational spectrum of the ligand upon complexation is a decrease in the wavenumbers of the band associated with B—N stretching, e.g. in (Me3N3B3Me2Ph)Cr(CO)3 this is at 1371 cm , compared to 1423 cm-1 in the free ligand. 

As its vibrational spectrum (vq-O = 961 cm ) did not allow an unambiguous assignment of the nature of the coordinated dioxygen (superoxo vs. peroxo), the crystal structure of the complex was determined. It revealed a dioxygen ligand coordinated in the side-on fashion... 

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