Spectra Orgel diagrams

Figure 108 Copper(III) ion (a) Orgel diagram and (b) the electronic spectrum of [CuF6]3 anion1347...

The Orgel diagrams illustrated in figs 3.11 and 3.12 indicate that, for electronic transitions between crystal field states of highest spin-multiplicities, one absorption band only is expected in the spectra of 3d1,3d4,3d6 and 3d9 cations in octahedral coordination, whereas three bands should occur in the spectra of octahedrally coordinated 3d2, 3d3, 3d7 and 3d8 ions. Thus, if a crystal structure is known to contain cations in regular octahedral sites, the number and positions of absorption bands in a spectrum might be used to identify the presence and valence of a transition metal ion in these sites. However, this method of cation identification must be used with caution. Multiple and displaced absorption bands may occur in the spectra of transition metal ions situated in low-symmetry distorted coordination sites. 

The electronic absorption spectrum of ]Ti(OH2)g] consists of two bands assigned to d-d transitions. Is this consistent with what is predicted from the Orgel diagram shown in Figure 21.20 Comment on your answer. 

If some of the solution of the product of photoreduction in Sec.9.4.2 is quickly dispensed into a vacuum 1 cm spectrophotometer cell and its spectrum is run over the visible range, a broad band appears at 460 nm. A similar band is seen in the Ti(III) solution prepared in Sec.9.3.1. An examination of the generalised Orgel diagram (Fig.A9.2) shows that in both octahedral or tetrahedral complexes, only one d-d transition is expected. On the other hand, the single u.v. band of the complex analysed in Sec.9.3.1 is due to ligand to metal charge transfer since no d-d transitions are expected. (Fig.A9.3 sketches all the possible electronic transitions for a metal complex). 

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