Ligands fields of

The ligand field of a quasi-octahedral coordination sphere acting on the (i-orbitals lifts the degeneracy of the excited spin quartet (and others) as sketched in tier (3). The nature of the resulting states and their energy depends on the strength... 

Nevertheless, despite the discouraging predictions of the early calculations, some attempts were made to apply the ligand field model to sandwich complexes. The first approach on these lines, due to Matsen (28), assumed a strong ligand field of D h symmetry, which was shown to split the d-orbital manifold into three levels characterised by the value of m. Unfortunately, the calculated energetic order for the metallocenes was found to be... 

As a consequence of the weak ligand field of (L19)2-, the Mn11, Fe11, Co11, and Ni11 ions in the acetato-bridged complexes 61-63... 

In the ternary complexes [Fe(127)(CN)2] the normally pentadentate macrocyclic aza-terimine ligand is only tetradentate, thanks to the particularly advantageous combined ligand field of two cyanide ligands and four nitrogen donor atoms in octahedral geometry. ... 

Quantum yield data for photochemically initiated ligand exchange reactions of a number of chromium(III) complexes having ligand fields of effective Oh symmetry are given in Table III. These data show that... 

If the ligand field of a ferric complex is weak, it will not be large enough to compensate for the exchange energy, which tends to align the spins of the elec-... 

Figure 2 Energy levels of high-spin chromium(II) in ligand fields of Oh and D4h symmetry...

The calculation of spin—orbit coupling effects in d" configurations in the presence of ligand fields of lower than cubic symmetry becomes a rather involved exercise. This occurs to a large extent because second-order terms become of importance, particularly in the interpretation of magnetic properties. 

The spin state of six-coordinate Fem(Por)LL varies from low to high and depends on the ligand fields of L and L. 20,87... 

The ligand field of the macrocycle is also modified by ring distortion.154 The metal to alkylated nitrogen distance is 2.33 A (Fe) to 2.53 A (Zn) which is considerably longer than the normal value of 2.0-2.1 A for the first row transition metalloporphyrins in a high spin state, while the extension is small for the other three M—Npor bonds. The reduced and distorted ligand field of the macrocycle makes it possible for even the Co complexes as well as other metals to take a high spin state. 

The size of the macrocycle coordination hole has a profound influence on its coordination chemistry thus in the weak ligand field of hydroporphyrinoid systems Ni2 + assumes the high spin state and binds extra axial ligands, while in the stronger ligand field of the corrin macrocycle the coordination sphere of the metal is saturated and diamagnetic complexes are generated [82]. 

Fig. 1. Term system for Cr3 + in a ligand field of Oh symmetry, as depicted by Schlafer and Gliemann (2G is the only one of the doublet terms shown). Reprinted with permission from Ref. [1], p 44, Fig. A32...

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