D Orbitals in octahedral complexes

FIGURE 10-20 Energies of d Orbitals in Octahedral Complexes Sigma-Donor Ligands. A, =... 

Fig. 20-10. Sketches showing the unique ground-state occupancy schemes for d orbitals in octahedral complexes with d configurations d1, d2, d3, ds, d9, d10.

Figure 1 Occupancy of d orbitals in octahedral chromium(Il) complexes...

Similarly, when a metal ion is surrounded by four tetrahedrally arranged ligands, as shown in Figs. 8.1.3 and 8.1.4, it is not difficult to see that in this case the electrons tend to occupy the dz2 and dx2 y2 orbitals in preference to the other three orbitals, dxy, dK, and dxz. The splitting patterns for a set of d orbitals in octahedral and tetrahedral complexes are summarized in Fig. 8.1.5. 

On the other hand, octahedral complexes of Ni(XI) and Cu(II) should be relatively unstable, since in such complexes electrons would have to occupy the higher-energy d orbitals. Indeed, octahedral complexes of Ni(II) and Cu(II) are rare those that exist are thought to be irregular octahedra with two of the groups (tram to each other) lying significantly farther from the central atom than do the other four. For these two metal ions, square complexes are by far the more usual. 

In general, tetrahedral complexes have more intense absorptions than octahedral complexes. This is a consequence of the first (Laporte) selection rule (Section 11-3-1) transitions between d orbitals in a complex having a center of symmetry are forbidden. As a result, absorption bands for octahedral complexes are weak (small molar absorptivi-ties) that they absorb at all is the result of vibrational motions that act continually to distort molecules slightly from pure symmetry. 

Crystal field theory was developed, in part, to explain the colors of transition-metal complexes. It was not completely successful, however. Its failure to predict trends in the optical absorption of a series of related compounds stimulated the development of ligand field and molecular orbital theories and their application in coordination chemistry. The colors of coordination complexes are due to the excitation of the d electrons from filled to empty d orbitals d-d transitions). In octahedral complexes, the electrons are excited from occupied t2g levels to empty Cg levels. The crystal field splitting Ao is measured directly from the optical absorption spectrum of the complex. The wavelength of the strongest absorption is called Amax and it is related to Ao as follows. E = hv, so Ao = hv = Because en-... 

Orbital diagrams for the d through d ions in octahedral complexes show that both high-spin and low-spin options are possible only for d", d, d, and d ions (Figure 22.23). With three lower energy t2g orbitals available, the d, d", and d ions always form high-spin complexes because there is no need to pair up. Similarly, d and d ions always form high-spin complexes because the t2g set is filled with six electrons, the two e orbitals must have either two (d ) or one dfi) unpaired electron. 

Thus far we have considered the crystal-field model only for complexes having an octahedral geometry. When fliere are only four ligands about the metal, the geometry is generally tetrahedral, except for the special case of metal ions with a d electron configuration, which we will discuss in a moment The crystal-field splitting of the metal d orbitals in tetrahedral complexes differs from that in octa-... 

Since the splitting of the d orbitals in tetrahedral complexes is much smaller than in the octahedral ones, the former appear, by and large, with high-spin configurations. Examples of tetrahedral complexes with low-spin configurations can be found only for metal ions with high oxidation states. 

Orbital diagrams for through d ions in octahedral complexes show that high-spin and low-spin options are possible only for d", d, d, and d ions (Figure 22.23). With three t2g orbitals available, d, d, and (P ions always form... 

Warren KD (1984) Calculations of the Jahn-Teller Coupling Constants for d Systems in Octahedral Symmetry via the Angular Overlap Model. 57 119-145 Warren KD (1977) Ligand Field Theory off-Orbital Sandwich Complexes. 33 97-137 Warren KD (1976) Ligand Field Theory of Metal Sandwich Complexes. 27 45-159 Watson RE, Perlman ML (1975) X-Ray Photoelectron Spectroscopy. Application to Metals and Alloys. 24 83-132... 

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