Octahedral complexes Orgel diagrams

The foregoing results for d1, high-spin d4 and d6, as well as d9 octahedral complexes can be summarized by the fairly simple Orgel diagram shown in Fig. 8.5.2. 

Additionally, we note that octahedral and tetrahedral complexes have opposite energy orderings (Fig. 8.1.5). Hence d1 octahedral and d9 tetrahedral have the same Orgel diagram the same is true for d6 octahedral and d4 tetrahedral complexes. In other words, the Orgel diagram in Fig. 8.5.2 is also applicable to d1, d4, d6, and d9 tetrahedral complexes. Since tetrahedral complexes are not centrosymmetric, their states do nothave g or u designations. States in Fig. 8.5.2 do not carry subscripts they should be put back on for octahedral complexes. 

The Orgel diagram for a high-spin d5 octahedral complex. 

This is a d3 complex with a tetragonal structure with /J4h symmetry. (Strictly speaking, this system has /J211 symmetry.) Hence the Orgel diagram shown in Fig. 8.5.5 no longer applies. If we assume this cation has an elongated octahedral... 

Correlation diagram for a d2 octahedral complex. The g subscript is omitted in all the state or orbital designations. Note that the lines connecting the triplet states constitute the Orgel diagram shown in Fig. 8.5.4 or Fig. 8.5.5. 

Figure 14.1 A generalised Orgel diagram for octahedral complexes with 2,3, 7 (high spin) or 8 d electrons.

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). 

---