Orgel diagram
Encyclopedia
Orgel diagrams are correlation diagrams which show the relative energies of elecronic terms
in transition metal
complexes, much like Tanabe-Sugano diagram
s. They are named after their creator, Leslie Orgel
. Orgel diagrams are restricted to only show weak field (i.e. high spin
) cases, and offer no information about strong field (low spin) cases. Because Orgel diagrams are qualitative, no energy calculations can be performed from these diagrams; also, Orgel diagrams only show the symmetry states of the highest spin multiplicity instead of all possible terms, unlike a Tanabe-Sugano diagram. Orgel diagrams will, however, show the number of spin allowed transitions, along with their respective symmetry designations. In an Orgel diagram, the parent term (P, D, or F) in the presence of no ligand field is located in the center of the diagram, with the terms due to that electronic configuration in a ligand field at each side. There are two Orgel diagrams, one for d1, d4, d6, and d9 configurations and the other with d2, d3, d7, and d8 configurations.
In an Orgel diagram lines with the same Russell – Saunders terms will diverge due to the non-crossing rule, but all other lines will be linear. Also, for the D Orgel diagram, the left side contains d1 and d6 tetrahedral and d4 and d9 octahedral complexes. The right side contains d4 and d9 tetrahedral and d1 and d6 octahedral complexes. For the F Orgel diagram, the left side contains d2 and d7 tetrahedral and d3 and d8 octahedral complexes. The right side contains d3 and d8 tetrahedral and d2 and high spin d7 octahedral complexes.
Term symbol
In quantum mechanics, the Russell-Saunders term symbol is an abbreviated description of the angular momentum quantum numbers in a multi-electron atom. It is related with the energy level of a given electron configuration. LS coupling is assumed...
in transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
complexes, much like Tanabe-Sugano diagram
Tanabe-Sugano diagram
Tanabe-Sugano diagrams are used in coordination chemistry to predict absorptions in the UV and visible electromagnetic spectrum of coordination compounds. The results from a Tanabe-Sugano diagram analysis of a metal complex can also be compared to experimental spectroscopic data...
s. They are named after their creator, Leslie Orgel
Leslie Orgel
Leslie Eleazer Orgel FRS was a British chemist.Born in London, England, Orgel received his B.A. in chemistry with first class honours from Oxford University in 1949...
. Orgel diagrams are restricted to only show weak field (i.e. high spin
Spin states (d electrons)
Spin states when describing transition metal coordination complexes refers to the potential spin configurations of the metal centers d electrons. In many molecules these spin states vary between high-spin and low-spin configurations...
) cases, and offer no information about strong field (low spin) cases. Because Orgel diagrams are qualitative, no energy calculations can be performed from these diagrams; also, Orgel diagrams only show the symmetry states of the highest spin multiplicity instead of all possible terms, unlike a Tanabe-Sugano diagram. Orgel diagrams will, however, show the number of spin allowed transitions, along with their respective symmetry designations. In an Orgel diagram, the parent term (P, D, or F) in the presence of no ligand field is located in the center of the diagram, with the terms due to that electronic configuration in a ligand field at each side. There are two Orgel diagrams, one for d1, d4, d6, and d9 configurations and the other with d2, d3, d7, and d8 configurations.
| Orgel diagrams | |
|---|---|
| Figure 1: D Orgel Diagram | Figure 2: F and P Orgel Diagram |
In an Orgel diagram lines with the same Russell – Saunders terms will diverge due to the non-crossing rule, but all other lines will be linear. Also, for the D Orgel diagram, the left side contains d1 and d6 tetrahedral and d4 and d9 octahedral complexes. The right side contains d4 and d9 tetrahedral and d1 and d6 octahedral complexes. For the F Orgel diagram, the left side contains d2 and d7 tetrahedral and d3 and d8 octahedral complexes. The right side contains d3 and d8 tetrahedral and d2 and high spin d7 octahedral complexes.