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A resonance Raman intensity analysis of the metal-to-ligand charge-transfer (MLCT) transition for the rhenium compound Re(2-(2‘-pyridyl)quinoxaline)(CO)3Cl (RePQX) is presented. Photoinduced geometry changes are calculated, and the results are presented using the vibrational normal modes and the redundant internal coordinates. A density functional theory calculation is used to determine the ground-state nonresonant Raman spectrum and a transformation matrix that transforms the redundant internal coordinates into the normal modes. The normal modes 37(rhenium coordination sphere distortion) and 75(ligand skeletal stretch) show the largest photoinduced geometry change ( 1.0 and 0.7, respectively). A single carbonyl mode is enhanced in the resonance Raman spectra. Time-dependent density functional theory is used to calculate excited-state geometry changes, which are subsequently used to determine the signs of the photoinduced normal mode displacements. Transforming to internal coordinates reveals that all the CO bond lengths are displaced in the excited state. The Re−C and C−C ligand bond lengths are also displaced in the excited state. The results are discussed in terms of a simple one-electron picture for the electronic transition. Many bond angles and torsional coordinates are also displaced by the metal-to-ligand charge transfer, and most of these are associated with the rhenium coordination sphere. It is demonstrated that using internal coordinates presents a clear picture of the geometry changes associated with photoinduced electron transfer in metal polypyridyl systems. [ABSTRACT FROM AUTHOR]

The lowest energy transition of Ru(CN)4(ppb)2-(ppb dipyrido2,3-a:3‘,2‘-cphenazine), a metal-to-ligand charge transfer, has been probed using resonance Raman spectroscopy with excitation wavelengths (488, 514, 530, and 568 nm) spanning the lowest energy absorption band centered at 522 nm. Wave packet modeling was used to simultaneously model this lowest energy absorption band and the cross sections of the resonance Raman bands at the series of excitation wavelengths across this absorption band. A fit to within ±20% was obtained for the Raman cross sections, close to the experimental uncertainty which is typically 10−20%. values of 0.1−0.4 were obtained for modes which were either localized on the ppb ligand (345−1599 cm-1) or the CN modes (2063 and 2097 cm-1). DFT calculations reveal that the resonance Raman bands observed are due to modes delocalized over the entire ppb ligand. [ABSTRACT FROM AUTHOR]

IR spectroscopy in concert with DFT calculations and resonance Raman spectroelectrochemistry has been used to identify the molecular orbital nature of the singly occupied molecular orbital (SOMO) in reduced Re(CO)3Cl(L) and Re(CO)3(4-Mepy)(L)complexes, where L 1,10-phenanthroline and its 4,7-diphenyl- and 3,4,7,8-tetramethyl-substituted analogues. The SOMO of each reduced species considered was found to be of b1symmetry, rather than the close lying orbital of a2symmetry (within a C2vsymmetry description of the phenanthroline moiety). This was deduced in a number of ways. First, the average carbonyl band force constants (kavkavreduced complex − kavparent complex) range from −57 to −41 N m-1for the series of compounds studied. The value of kavrelates to the extent of orbital overlap between the ligand MO and the metal d MO. These values are consistent with population of a b1MO because the wave function amplitude at the chelating nitrogens for this MO is significantly greater than that for a2MO. Second, calculations on singly reduced Re(CO)3(4-Mepy)(phen)and Re(CO)3(4-Mepy)(tem)predict population of a b2SOMO. The spectra predicted for these species are in close agreement with the vibrational spectroscopic data; for the IR data the shifts in the CO bands are predicted to 6 cm-1and the mean absolute deviation between calculated and measured Raman bands was found to be 10 cm-1. [ABSTRACT FROM AUTHOR]