Inter-valence charge-transfer

IVCT = inter valence charge-transfer LMCT = ligand-to-metal charge-transfer MLCT = metal-to-ligand charge-transfer MRI = magnetic resonance imaging... 

When we have two metal ions in different oxidation states, we can have inter valence charge transfer. The interplay between Fe " and Ti" causes the blue in blue sapphire and blue kyanite but also makes dravite brown Mn " and Ti " combine to cause elbaite to be yellow. 

Titanium, in quantities sufficient for luminescence, has been found in the kyanite samples that were studied (Chadwick and Rossman 2009). It is agreed that the oxidation state of Ti in kyanite is 4+ and that the blue kyanite color comes from Fe -Ti inter-valence charge transfer (Platonov et al. 1998). Ti " " is not a generally stable oxidation state in terrestrial rocks (Waychunas 1987), however, instances of its occurrence are established, often due to the effects of naturally occurring ionizing radiation. 

Photochemical studies of iron-group metallocene substrates have received much attention, e.g. quenching of excited uranyl ion luminescence, formation of charge-transfer complexes with TCNE, redox reactions of octamethyl-ferrocene and of carboxylate anions of the types FcCOj and Fc(X)COr (X = saturated or unsaturated alkyl chain). Enzyme-catalysed one-electron oxidation of ferrocene derivatives has also been studied. Ferrocene-ferricenium cation redox systems have been incorporated into electrochemical and photo-electrochemical cells, and have found use for catalysis of photo-addition of MeOH to Bu NCO. Inter-valence electron-transfer properties of partially oxidized Fc(C C)nFc ( = 0—2), meso-tetraferrocenylporphyrin, and poly(vinylferrocene) have been assessed. 

This empirical equation (when corrected for the effects of inter-electronic repulsion and for differences in the ligand field splitting) allows one to predict the frequencies of charge transfer bands for a great variety of complexes . Remarkable information on redox properties can be obtained from the parameters of the Jorgensen equation because they are roughly proportional to valence state ionization potentials of the metal and to the ionization potentials of the ligands. 

Figure 15.18 Complexes that show inter-valence bands and ligand-to-hgand charge transfer absorption bands.

In four dendrimers terminated by 12 electroactive tetrathiafulvalenyl substituents (160), the three dimensional character of the inter- and intra-den-drimeric charge and eleetron transfer, and hence of the eleetroconductivity, has been assessed by examination of the electronic spectra of their corresponding neutral state and nation, radieal, dication, and mixed-valence salts, including a closed - shell anion (Figure 24). ... 

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