Ligand-to-metal charge transfer band

Another possible route for reduction of the iron center is photoreduction. This has been studied in a variety of marine siderophore systems, such as aquachelin, marinobactin, and aerobactin (2), where it was demonstrated that photolytic reduction was due to a ligand-to-metal charge transfer band of the Fe(III)-siderophore complex, eventually resulting in reduction ofiron(III) and cleavage of the siderophore (31,154,155). This suggests a possible role for iron reduction in iron release (71,155). 

The visible spectra of oxyHr and metIh N3 are dominated by ligand-to-metal charge transfer bands from the hydroperoxide or azide anions, but otherwise they are similar to those of the synthetic complexes (Rgure 2) (38). The d-d transitions observed at 700 and KXX) nm are more intense than usually observed for high-spin iron(llI) complexes, probably due to the strong antiferromagnetic coupling interaction (38,40). 

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

The piezochromism of [Fe(CN)5(4CNpy)] and [Fe(CN)5(pz)] (and of the biferrocenium cation) was included in a wide-ranging solvatochromism/piezochromism correlation for metal-to-ligand (and ligand-to-metal) charge-transfer bands of a variety of inorganic and organometallic complexes. 

The solvatochromism of the ligand-to-metal charge-transfer bands of [Fe (CN)5L] with L = (substituted) imidazoles and pyrazoles has been described. " ... 

The type-1 blue copper proteins act as electron carriers azurin, plastocyanin, stellacyanin, umecyanin e.g. They are characterized by a rather strong LMCT (ligand to metal charge transfer) band near 600 nm and by small hyperline coupling constants A in EPR. Copper is bound to two imidazole groups of histidine and to two... 

The assignment of these main bands to n - n transitions was confirmed by MO calculations and MCD studies.179,598 For the first row transition metals with vacancies in dxz and dyi orbitals, a ligand to metal charge transfer band is observed at 380-500 nm.200 A weaker metal to ligand charge transfer band is also expected to occur in this region. 

The absorption spectra of (rans-[RuX2(L)]+ (L = 454-456,458,459, X = Cl-, Br ", I-) show two ligand to metal charge transfer bands. Irradiation at the lower energy CT band leads to stereoreten-tive aquation of X- the effects of L on the photoreactivity of these complexes have been discussed and related to their open chain analogues.642... 

LMCT ligand-to-metal charge transfer band... 

EXAFS data on bromoperoxidase (48) point to backscattering from light atoms, which may be due to histidine coordination or the presence of a tyrosine. However, intense ligand-to-metal charge-transfer bands in the visible spectra, such as those seen in mono-oxovanadium(V) phenolates (66-69), have not been observed in bromoperoxidase (15,16, 19). Thus, the proposal (48) of a tyrosine residue coordinated to vanadi-um(V) in bromoperoxidase is not very likely. In fact, the tailing observed (15,16,19) in the absorbance spectrum of bromoperoxidase from 280 to 350 nm may be due to the absorbance of vanadate (56) incorporated in the enzyme. 

This is in ample accord with the fact that the Cg orbitals with a considerable 3 d character have a large interelectronic repulsion term (condition ii) and that this same term is small in the antibonding 6g orbital, which is mainly a ligand orbital (condition iii). The ligand-to-metal charge transfer band is described in the new scheme as a e -> 6g transition, not as a -> transition, but, of course, it is the e orbital that is now a predominantly ligand orbital. 

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