Crystal field activation energies

There have been few studies of substitution in complexes of nickel(II) of stereochemistries other than octahedral. Substitution in 5-coordinated and tetrahedral complexes is discussed in Secs. 4.9 and 4.8 respectively. The enhanced lability of the nickel(II) compared with the cobalt(II) tetrahedral complex is expected from consideration of crystal field activation energies. The reverse holds with octahedral complexes (Sec. 4.8). 

Crystal Field Activation Energies (in Dq Units) for Associative (OW and PBP) and Dissociative (SQP and TBP) Substitution Reactions of High-Spin Octahedral Complexes... 

Table 8.2. Crystal field activation energies for substitution reactions... 

Table I. Octahedral Crystal Field Activation Energies"...

For first-row metals (+ 2), an extra destabilization due to electrons in eg orbitals accounts for a ligand labilization. This effect is commonly referred to as crystal field activation energy (CFAE) [1 a—c]. 

It is difficult to evidence pure cases of inner sphere complex formation between surface groups and transition metal ions (also called "grafting") since other phenomena are usually occurring in parallel. The clearest instances are observed when "spectator" ligands are inert to substitution, either because of chelate effects (ds- [Ni(en)2(H20)2p on various supports ) or because of high crystal field activation energies ([Co(NH3)5(RO)] + on TiAl2C)3 RO= OH, H2O or alcohol). 

Vanadium(II) has a electron configuration, but rarely shows the high crystal field activation energy which might be expected. This has been demonstrated once again, in the course of electrochemical studies of various polypyridyl complexes. Stopped-flow techniques are indicated for substitution here. " ... 

Technetium(IV) is an oxidation state where high crystal field activation energies may be expected, and indeed substitution at [TcBrg] " and at [TcF ] " is very slow. Under forcing conditions the latter gives di-/i.-oxo-di-technetium species, indicating a complex mechanism. The much-studied and much-used... 

Stereochemical changes taking place in the course of substitution reactions of octahedral complexes have been reviewed. An improved method for estimating crystal field activation energies has been described. ... 

Table 3.15. Crystal Field Activation Energies for Two Transition States with High-Spin Configurations in Units of Dq...

Table 3.16. Water Exchange Rate Constants (2S°C), Activation Parameters and Predicted Crystal Field Activation Energies for First-Row Transition-Nfetal Ions...

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