Weak-field case

The foregoing discussion applies to complexes that are weak-field cases. Spectral analysis for strong-field cases is somewhat different and will not be discussed here. For complete analysis of the spectra of strong-field complexes, see the book by A. B. P. Lever, Inorganic Electronic Spectroscopy, listed in the references at the end of this chapter. 

A = 1 in the strong ligand field limit, 1.5 in the weak field case. For T2 ) terms, L remains at unity. 

SOLUTION (a) In the strong-field case, all five electrons enter the t2g-orbitals and to do so, some of them must pair (20). There is one unpaired electron in this configuration, (b) In the weak-field case, the five electrons occupy all five orbitals without pairing (21). There are now five unpaired electrons. 

Figure 14.1. The splitting and re-labeling ofaP1 2P term in a crystal field of 4mm symmetry. On the LS, IIs.i, < He, (see eqs. (14.3.15) and (14.3.20). The RS shows the weak-field case when Hcf < IIS. The degeneracy of each state is shown in parentheses.

The modeling of the low-lying energy levels for a weak-field case is shown in Fig. 44, and one can draw the following conclusions. 

Considering only the dipole term in the interaction energy (the weak-field case)... 

For the weak field case, we have the situation where the crystal field interaction is much weaker than the electronic repulsion. In this approximation, the Russell-Saunders terms 3F, 3P, 1G, lD, and 5 for the d2 configuration are good basis functions. When the crystal field is turned on, these terms split according to the results given in Table 8.4.2 ... 

The weak-field case like the free ion obeys Hund s rule while in the strong-field case Hund s rule is overcome by the increased relative stability of the t-type relative to the e-type orbitals... 

A third case arises when the perturbation from the ligand field is intermediate between the weak-field case and the strong-field case. There is no sharp dividing line between the three cases given here. The calculational approach to be used depends on the identities of the transition metal ion and the ligands. The results of this third case have been presented by Figgis. Applications have also been discussed by Mabbs and Machin. ... 

SO there is no difference in the net spin of the electrons for strong- and weak-field cases. On the other hand, the through ions exhibit high-spin and low-spin states, as shown in Table 10-5. Strong ligand fields lead to low-spin complexes, and weak ligand fields lead to high-spin complexes. 

FIGURE 10-27 Angular Overlap Energies of four- and six-Coordinate Complexes. Only ct bonding is considered, (a) Octahedral and square-planar geometries, both strong- and weak-field cases. 

The complex [Cr(CN)6] is an example of a strong field complex, whereas [Cr(H20)g] is a weak field case. There are N—A electrons to be, attributed corresponding to a sub-configuration of Cr " ". The (lowest... 

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