Electronic spectra of octahedral and tetrahedral complexes

Similar splittings occur in a tetrahedral field, but the g labels are no longer applicable. 

For the d configuration (e.g. Cu ) in an octahedral field (actually, a rare occurrence because of Jahn-Teller effects which lower the symmetry), the ground state of the free 

In order to work out the terms for the d configuration, a table of microstates (Table 21.7) must be constructed. However, for interpreting electronic spectra, we need concern ourselves only with the terms of maximum spin multiplicity. This corresponds to a weak field limit. For the d ion, we therefore focus on the E and (triplet) terms. These are summarized in Table 21.9, with the corresponding microstates represented only in terms of electrons with = +. It follows from the rules given in Section 21.6 that the term is expected to be lower in energy than the P term. In an octahedral field, the P term does not split, 

Bussiere, H. Belisle and C. Reber (2000) J. Chem. Ed., vol. 77, p. 670 http //jchemed.chem.wisc.edu/JCEWWW/ Articles/JCENi/JCENi.html] 

The electronic spectrum of an aqueous solution of [Ni(en)3] exhibits broad absorptions with A ax 325, 550 and 900 nm. (a) Suggest assignments for the electronic transitions, (b) Which bands are in the visible region  

Each transition is spin-allowed (no change in total spin, S) and the electronic spectrum of each ion exhibits one absorption. For sake of completeness, the notation for the transitions given above should include spin multiplicities, 25 + 1 (see Box 20.6), e.g. for octahedral J, the notation and for high-spin, octahedral d, 7 2 -s— Eg. 

In an analogous manner to grouping j, d , d° and J ions, we can consider together d, d, d and d ions in octahedral and tetrahedral fields. Two terms arise for the d ion E (ground state) and (excited state) deriving terms from a table of microstates is dealt with in the next subsection. In an octahedral field, the P term does not split, and is labelled The E term splits into 

For the high-spin configuration, all transitions are spin-forbidden and d-d transitions that are observed are between 

For a proper interpretation of electronic spectral features, interelectronic interaction must be taken into account and parameters additional to are needed to quantify the description of the spectrum. There are Racah parameters which we shall meet again when we describe Tanabe-Sugano diagrams. The evaluation of from electronic spectra is, therefore, more difficult for d (and related d ) than for (and etc.) ions and some uncertainty is often associated with reported values. 

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