Intervalence charge transfer effects

The mixed-valence ion has an intervalence charge transfer band at 1562nm not present in the spectra of the +4 and +6 ions. Similar ions have been isolated with other bridging ligands, the choice of which has a big effect on the position and intensity of the charge-transfer band (e.g. L = bipy, 830 nm). 

The effects of temperature on the shape of intervalence charge-transfer bands for the radical cations of bis(2-f-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl)hydrazines that are bridged by 2,5-xylene-1,4-diyl, durene-l,4-diyl, naphthalene-1,4-diyl, biphenyl-4,4-diyl and 9,9-dimethylfluorene-2,7-diyl aromatic rings were studied by ESR. ... 

Electronic Stark effect studies by Oh and co-workers revealed that intervalence absorption by the CT ion is accompanied by essentially zero change in dipole moment and, therefore, zero metal-to-metal charge transfer. The observations are consistent with a description of the complex as fully delocalized in both the ground state and intervalence excited state. At the same time, the researchers found that intervalence excitation of (NH3)sRu(/Lt-4,4 -bipyridine)Ru(NH3)5 is accompanied by a large change in dipole moment and, therefore, substantial transfer of charge between metal centers, consistent with a valence-localized description. 

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