Ligand-metal charge transfer complexes

The u.v.-visible spectra of [Pt2X6]2- (X = Cl or Br) have been measured 14 the band assignments include ligand- metal charge-transfer and d— p bands, in addition to the low-intensity d- -d bands. The purple vapour complex formed from [Pt6Cl12] solid cluster and gaseous A1C13 has been studied spectrophotometrically.120... 

There are many other Prussian blue analogs for which the visible spectrum is complex and not understood. Heavy metal ferricyanides and hexacyano complexes of other transition metals with less than d configurations are in this class due to the presence of ligand-metal charge transfer processes. 

The chelation effect of Cys-X-Y-Cys was also found for the MCD spectra of Fe(III) complexes of Z-Cys-Pro-Leu-Cys-OMe or Z-Cys-Ala-Ala-Cys-OMe, which exhibited a characteristic ligand-metal charge transfer (LMCT) at 350 nm, but not for those of the Fe(III) complex of Z-Ala-Cys-OMe, Z-Cys-Ala-Cys-OMe, or S2-o-xyl (28). The MCD spectral differences in the region of 300-400 nm are related to the difference in the electronic states of the Fe(III) singly occupied metal t2 orbitals affected by the lone pair on the sulfur atom. The possibility of a spectroscopic splitting by a specific Cys-thiolate orientation relative to other Fe-S bondings has been predicted theoretically by Bair and Goddard (29). The orientation of n orbitals of the sulfur lone pair is now found to be determined by the peptide conformation which dictates the steric disposition of the S-C bond. 

Platinum(IV) is an oxidant therefore, ligand-metal charge-transfer (LMCT) transitions are prominent in the electronic spectra of its complexes and play important roles in the photosubstitution chemistry. This is especially true for the hexahalo complexes, [PtXj]. The aqueous hexachloroplatinate(IV) ion, [PtCl ] , undergoes both photoaquation ... 

Charge-transfer transitions may occur in the case of covalently bound ligand orbitals and empty or anti-bonding metal orbitals. Organic ligands forming charge transfer complexes are often used in the analysis of ions such as Fe, Cu, Cd or Zn. 

We have found that the paramagnetism of these complexes is temperature independent as expected for the singlet ground state predicted by the MO theory with M -M bonding. The assignment of the bands in the optical spectrum is complicated because there are three types of transitions possible and these must be sorted out first. The ligand metal charge transfer bands are... 

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