Diimines charge transfer

Low-valence transition metal complexes of a-diimine ligands are highly colored because of the presence of low-energy metal to a-diimine charge transfer (MLCT) transitions. For a series of d6-M(CO)., (a-diimine) (M=Cr,Mo,W) and d8- M (CO)3 (a-diimine) (M =Fe, Ru) complexes, we have studied the spectroscopic and photochemical properties (1-10). The a-diimine ligands used are 1,4-diaza-1,3-butadiene (R-DAB), pyridine-2-car-baldehyde-imine (PyCa), 2,2 -bipyridine (bipy) or 1,10-phenanthroline (phen) molecules. A close relationship was deduced between the photochemical behavior of these complexes and their resonance Raman (rR) spectra, obtained by excitation into the low-energy MLCT band. 

Electronic and vibrational spectroscopy continues to be important in the characterization of iron complexes of all descriptions. Charge-transfer spectra, particularly of solvatochromic ternary diimine-cyanide complexes, can be useful indicators of solvation, while IR and Raman spectra of certain mixed valence complexes have contributed to the investigation of intramolecular electron transfer. Assignments of metal-ligand vibrations in the far IR for the complexes [Fe(8)3] " " were established by means of Fe/ Fe isotopic substitution. " A review of pressure effects on electronic spectra of coordination complexes includes much information about apparatus and methods and about theoretical aspects, though rather little about specific iron complexes. ... 

The D, A or PS units may be metal coordination centres. Metal to ligand charge transfer (MLCT) in metal complexes (such as Ru(n) or Re(l)-diimine centres) has been extensively used for generating PeT processes [8.64-8.68, A. 10, A.20]. Our own work has been concerned with photoinduced charge separation in macropoly-cyclic coreceptors containing both a photosensitive porphyrin group and binding sites for silver(i) ions as acceptor centres. Thus, complexation of silver ions by the... 

Fig. 10 Charge-transfer-to-diimine emission bands of the dbbpy series of complexes 16-21 with varying dithiolate (top), and the toluenedithiolate series 21-28 with varying diimine (bottom). The spectra were recorded in frozen butyronitrile at 77 K their intensities have been normalized. Reprinted with permission from [43]. (1996) American Chemical Society...

Keywords rhenium carbonyl diimine photophysics excited state electron transfer charge transfer relaxation intersystem crossing DFT time-resolved IR spectroscopy... 

The most detailed spectroscopic and electronic structure studies of metallo-mono(dithiolenes) have focused on the nature of ligand-to-ligand charge transfer (LLCT) excitations in [M(diimine)(dithiolene)] complexes (112, 250-257, 262, 264, 295-301) and in monooxo molybdenum dithiolenes (19, 20, 22, 23) as models for pyranopterin molybdenum enzymes such as sulfite oxidase (SO). Since metallo-mono(dithiolenes) generally possess little or no symmetry, detailed spectrosopic and electronic structure studies of this class of metallo-dithiolenes have only recently begun to appear. The analysis of the spectroscopic data has been aided by the fact that the dithiolene-to-metal charge... 

Figure 4. (a) Charge-transfer-to-diimine absorption bands for Pt(tmphen)(tdt) (17), Pt(dbbpy)(tdt)... 

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