Charge transfer to ligand

Are these bands more likely due to charge transfer to metal or charge transfer to ligand Explain briefly. (Reference F. Hard and A. Vlcek, Jr., Inorg. Chem., 1996, 35, 1257.)... 

Unusual Properties of Charge-Transfer-To-Ligand (CTTL) Excited States... 

Formation An approach to form QM complexes in which the QM ligand is coordinated only via the exocyclic C=C bond and can be released from the metal was developed by Milstein.18,19 The synthetic strategy is based on the idea that a zwitterionic t -methylene-p-phenoxy metal complex may undergo charge transfer to the metal, resulting in an ri2-methylenep-QM complex of the reduced metal center (Scheme 3.9). 

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

Photoirradiation or heat treatment is also applied for the reduction of metal ions. In these cases, enough energy to cleave the metal-ligand bond is required for the reduction. Theoretically, the absorption band attributed to the charge transfer from ligand to metal must be excited by the photoirradiation. The coexistence of alcohol can assist the photoreduction. In this case, the corrdination of the alcohol to metal ions may decrease the reduction potential, or the ketyl radical produced may reduce the metal ions as shown in Scheme 9.1.7. 

A second example is the recently reported singlet-triplet equilibrium in a Mo(II) complex, cis-[Mo(bipy)2(OPri)2] (31). The interpretation of the magnetism is complicated by the possibility that the equilibrium is not entirely metal centered, but involves charge transfer to the bi-pyridyl ligands. Because a strong field is required to spin pair the d4 configuration, however, it is not impossible that examples exist among Mo(II) chemistry. The possible dynamics are subject to considerations similar to those which apply to Mn(III). 

Figure 4.75 Schematic representation of the charge transfer in various excited states of a metal complex. M is the metal centre and L stands for a ligand. LF is a ligand field transition, CTs are the charge transfer transitions, LL is an intraligand transition, and CTTS is a charge transfer to solvent...

MLCT metal to ligand charge transfer LMCT ligand to metal charge transfer HOMO highest occupied molecular orbital AOM angular overlap model RHF restricted Hartree-Fock... 

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