Metal intraligand state

The excited states which are responsible for the eel of the previous examples are of the CTML type or involved in metal-metal bonding of polynuclear complexes. Photoluminescence, or eel in our case, can also originate from intraligand (IL) excited states provided these states are the lowest excited states of such complexes. IL emissions are characteristic for many transition metal... 

The transformation of RhCl(PH3)2(HC=CH) to RhCl(PH3)2(C=CH2) has been calculated (MP2) to be exothermic by 7.8 kcal.mol"1. The intraligand 1,2-hydrogen shift mechanism found in the Ru11 system is not relevant to the present rhodium case. Starting from a T 2 C=C complex, both systems give a metal-( T]2 C-H) species in a subsequent step. In the case of the d6 Ru system this ri2 C-H complex is an intermediate. In contrast, the T 2 C-H coordinated state is a transition state in the d8 Rh1 system, the oxidative addition being a very facile process. 

Intraligand (IL) excited states of coordination compounds arise from electronic transitions between molecular orbitals primarily localized on a coordinated ligand. It is difficult, a priori, to predict the reactivity of this type of state. While it is logical to expect ligand-centered reactions, the influence of the metal on such processes can be substantial and result in net photochemistry which differs from that of the free ligand. A few examples should serve to illustrate the range of IL photoreactions reported to date. 

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...

TDDFT calculations results were consistent with the band shapes of the optical spectra of the parent complexes and are shown in Fig. 14. The calculated optical transitions are shown as bars under the experimental spectra and consist of MLLCT, ligand-to-ligand charge transfer transitions (LLCT), intraligand n - tt transitions (IL), and metal-complex delocalized-charge transfer transitions (MCDCT). Triplet state energies were also calculated based on a3 MLLCT state and correlated with experimental emission spectral results [53]. 

The absorption spectra of [Pt(tpy)Cl]+ salts in solution show two sets of bands. Intense, structured bands occur at wavelengths less than about 350 nm, attributed to intraligand n-n bands similar to those shown by Zn(tpy)Cl2 [68]. The somewhat weaker bands in the 350-450 nm range are assigned to 1M LCT transitions they have no counterpart in the zinc complex, which acts as a model in which the metal center cannot be oxidized and where low-energy d-7r excited states are thus not possible. 

Figure 6.17(a) shows the time-resolved transient absorption spectra obtained for [Ru(dcbpy)2(bpzt)] in aqueous solution at pH 7. The important features are the bleaching of an absorption feature with a maximum at 450 nm and the growing in of a new band at 350 nm. The bleaching process can be attributed to the disappearance of the metal-to-ligand charge-transfer (MLCT) transitions in the excited state, while the feature at 350 nm is indicative of intraligand transitions of the dcbpy radical formed upon excitation of the complex. This type of behavior which is typical... 

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