Ligand-centered transitions

Rh(thpy)2en]+ and [Ir(thpy)2en] + in CH2C12 are very similar structured bands with intensity maxima between 18 200 cm 1 and 19 000 cm 1. They have been assigned to ligand centered transitions on the thpy ligands... 

Ligand-centered transitions (LC) occurring also in the free ligand. In the complex they are perturbed to a lesser or a greater degree, but not completely modified. 

Literally thousands of papers have been written describing the photochemical and photophysical properties of [Ru(bpy)3] + over the past several decades, making it one of the most widely studied compounds in the history of inorganic chemistry. The compound exhibits a rich electronic spectrum, with several high-energy n n ligand-centered transitions in the near-UV, weak LF absorptions around 400 nm, and a series of intense MLCT bands around 450 nm. Excitation of the MLCT bands leads... 

Figure 5 (a) Luminescence and excitation spectra of the MLCT transition of the Pt (bipyridine)(3,5-dimethylpyrazolate)2 complex in ethanol-methanol (3 1) frozen glass at 77 K. (b) Luminescence and excitation spectra of the ligand-centered transition of the protonated form of the complex in (a) in ethanol-methanol (3 1) frozen glass at 77 K (reproduced by permission of the American Chemical Society... 

Thus, SOC determines the C-term intensity, which is dependent on the magnitude of the SOC constant. Since the SOC constant will be greater for metal-centered than ligand-centered transitions, d excited states are expected to be more spin-orbit mixed than ligand-based charge transfer (CT) states and show larger low-temperature MCD intensity relative to absorption intensity. The MCD-to-absorption intensity ratio is often expressed as CajD, which is given experimentally by Equation (6) ... 

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