Halide-to-ligand charge transfer

Another important type of LLCT state arising in diimine rhenium(I) tricarbonyl complexes is found in IRe (CO)3(diimine) complexes. When I replaces Cl or Br, the lowest excited states changes from being MLCT in nature to that of XLCT (halide-to-ligand charge transfer) in character. Figure 2 clearly shows that the lowest energy band of the transient absorption... 

It is interesting to note that in the Os -n(NH3)n family (X = Cl, Br, 1- n = 2,3,4), where the measured change in the Os couple is of the same order (0.33 V/X-), the halide to metal charge-transfer bands do not shift appreciably as the stoichiometry alters. Clearly, this is well accomodated by our model. Thus, in addition to the familiar effects of the ligands on the metal center, a "ligand field theory for ligands" is required. The present analysis is an early step in the quantification of these terms. 

The same coordination geometry was also inferred from the analysis of the lowest energy LMCT bands (see Ligand-to-Metal Charge Transfer) in the far-UV absorption spectra of Zu7- and Cd7-MT, and those of corresponding tetrahedral halide complexes (see Cadmium Inorganic Coordination Chemistry see Zinc Inorganic Coordination Chemistry) Further support came from... 

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