Orbital Splitting Patterns

One reason that chemists evaluate the d orbital count is to determine if the metal complex is diamagnetic or paramagnetic. A diamagnetic complex has all electrons paired. NMR spectra with chemical shifts similar to organic compounds can be obtained for these structures. A paramagnetic complex has one or more unpaired electrons. Very often, standard NMR spectra for these structures cannot be obtained. Either the resonances are so broad that they cannot be detected, or the chemical shifts are spread over an unusually wide ppm range. 

Due to the unpaired electrons, paramagnetic compounds often react as radicals. In the section on oxidative addition below, we ll see that radical mechanisms can be involved. In fact, many organometallic mechanisms involve radicals, and having a knowledge of which orbitals these radicals reside in is informative. The identity of the singly occupied orbitals is predicted by an examination of the d orbital splitting. 

Another use of the d electron count is the determination of whether a metal has a nucleophilic orbital. Square planar complexes with d orbital counts above four have electrons in a dj2 orbital. This orbital is completely accessible because there are no ligands along the z axis. The orbital can act as a nucleophilic lone pair, much like a lone pair on a nitrogen atom. For example, in Rh(Cl)(CO)(PPh3)2, the metal is d and the complex is square planar. Hence, the structure is nucleophilic at Rh. However, the complex only has 16 electrons, and thus it is also electrophilic. This is not uncommon some inorganic and organometallic complexes can often accept and donate electrons, and the reactivity patterns reflect this. 

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IFIGU RE 17.6 The orbital splitting pattern in a tetrahedral field that is produced by four ligands. 

Thus, the ligand-stabilized d-orbital splitting pattern is qualitatively consistent with the expectation of crystal-field theory, but the physical origin of this splitting should be attributed to attractive donor-acceptor interactions such as (4.86b) rather than to any inherent electrostatic repulsions toward the incoming ligands. More accurate treatment of the spectroscopic 10Dq value should, of course, be based on separate consideration of the two spectroscopic states. 

As indicated earlier, a difficulty immediately arises the evaluation of the parts of the matrix elements (equation 4) involving terms containing r using free-ion d wave functions gives results which are obviously grossly in error. Consequently, there is not likely to be any relationship between the parameters such as developed in cubic symmetry the low symmetry cases involve (at least) three parameters to describe the d-orbital splitting pattern. 

Fig. 5.1. Common d-orbital splitting patterns in high spin iron(III) complexes of tetrahedral (Td), octahedral (Oh) and tetragonal (D4h or C4v) symmetries.

The d orbitals splitting patterns in (a) octahedral and (b) tetrahedral complexes. 

Referring to the orbital splitting pattern for an axially elongated tetragonal complex shown in Fig. 8.3.2, if we continue the elongation, the splittings... 

Correlation between the orbital splitting patterns of octahedral MLg and square-planar ML4 complexes. 

To determine the first-order spin-orbit splitting pattern of an orbitally degenerate electronic state, we shall make use of the energy expression obtained from the phenomenological operator, which in this case reduces to Aso A S because only the z component of the spin-orbit operator is involved. 

Figure 16 Spin-orbit splitting pattern of an j= 5/2 inverted 2D atomic state.

Fig. 16. Octahedral dA cw-(r)2-olefin)(i72-alkyne)ML4 dir orbital splitting pattern.

Fig. 20. Orbital splitting pattern for the four dir orbitals of trigonal bipyramidal dA Mo(HCsCH)(SR)2(CNR)2.

Fig. 22. Possible approximate relative d orbital splitting patterns for the metallocenes (left) and open metallocenes (right)...

By far the most common oxidation state for Ni is the -l-II state with a d electron configuration. Four, five, and particularly six coordination are all common geometries for nF and depend upon the ligands present. Scheme 1 shows the d-orbital splitting pattern for tetrahedral, square-planar, tetragonal, and octahedral nF. 

Repeat the same procedure for each of the other structures. The multiplicity with the lower UHF energy should indicate the preferred magnetic state for that simplified complex. How do these compare with your original predictions based on -orbital splitting patterns for the different geometries (Record in Results Summary section.)... 

Cashin el al. s explored the Lewis base properties of several vanadyl complexes, in which a Lewis acid interacts with the lone pairs on the V=0 oxygen, as shown in Figure 9.7. How would the addition of a Lewis acid capable of coordinating the oxygen change the d-orbital splitting pattern of the complex, and also the visible spectrum. 

The orbital splitting pattern for sandwich compounds is defined by two parameters Aj and A2 B and C are Racah parameters and (3 the nephelauxetic ratio. 

Most of the optical spectra of RhCl63 complexes are not well enough resolved to reveal details of the spin-orbit splitting pattern due to line broad-... 

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