Intervalence charge transfer IVCT transitions

D Alessandro DM, Keene FR (2006) Current trends and future challenges in the experimental, theoretical and computational analysis of intervalence charge transfer (IVCT) transitions. Chem Soc Rev 35 424 140... 

Fe2 - Fe3 Charge Transfer. Partial reduction of Fe3 clays results in Fe2 and Fe3 cations occupying edge-sharing Fe06 coordination polyhedra. Such a condition allows for optically (and perhaps thermally) induced intervalence charge transfer (IVCT) transitions ... 

Photoswitching of the electronic communication between two metal centers using the photochromic diarylethene bridging ligand with both thiophene moieties substituted with two cyclometallated phenylpyridines (Figure 23a) was first reported by Coudret and Launay. Although the comproportionation constants (Kc) for the dinuclear mixed-valence ruthenium complexes in both the open and closed forms were similar, the intervalence charge-transfer (IVCT) transitions were observed only in the closed... 

The uv/vis/nir spectra of mixed-valence species exhibit unique low-energy intervalence charge transfer (IVCT) transitions which are absent in the fully reduced and oxidised complexes. Qass (valence localised) mixed-valence systems have broad, weak, structureless IVCT bands which are sensitive to molecular environment (eg solvent ). Detailed study of these bands in trapped valence species allows os to calculate intramolecular electron transfer rates. Class III (valence delocalised) systems have more intense low-energy transitions which are often structured and are largely insensitive to solvent. We will consider the degree of metal-metal interactions within class III species by analysis of low-energy absorption transitions. 

The electronic spectra of a variety of transition metal-bearing oxide and silicate minerals have been measured at high pressures and/or elevated temperatures. Trends for absorption bands originating from crystal field (CF), metal-metal intervalence charge transfer (IVCT) and oxygen —> metal charge transfer (OMCT) transitions are summarized in tables 9.2,9.3 and 9.4, respectively. 

Vivianite, Fe2+3(P04)2.8H20, is the classic example of a mineral showing an intervalence charge transfer transition (Wherry, 1918 Bums, 1981). Vivianite has a diagnostic indigo-blue colour and a well characterized Fe2+ —> Fe3+ IVCT absorption band in the polarized spectra illustrated in fig. 4.12 and is the datum with which electron interaction parameters for other minerals are compared. The chemical formula of vivianite is not indicative of a mixed-valence compound. However, the pale-green colour of newly cleaved vivianite crystals or fleshly... 

Spectroelectrochemistry provides a convenient avenue to assess whether this conclusion is correct by allowing the isolation and spectroscopic smdy of the mixed valence state. Oxidation of the first metal center results in the formation of the mixed valence Ru(II)Ru(III) ion reflected in the grow-in of a new optical transition centered at 1700 nm (s = 2250 dm mol cm ) and identified as an intervalence charge transfer transition (IVCT). The optical characteristics of such transitions can be analyzed according to the Hush theory (21) and used to estimate the extent of electronic coupling between two metals across the intervening bridge. The full width at half maximum (FWHM) (Vj j) of the... 

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