Ligand field stabilization energy, effect

Many of the spinel-type compounds mentioned above do not have the normal structure in which A are in tetrahedral sites (t) and B are in octahedral sites (o) instead they adopt the inverse spinel structure in which half the B cations occupy the tetrahedral sites whilst the other half of the B cations and all the A cations are distributed on the octahedral sites, i.e. (B)t[AB]o04. The occupancy of the octahedral sites may be random or ordered. Several factors influence whether a given spinel will adopt the normal or inverse structure, including (a) the relative sizes of A and B, (b) the Madelung constants for the normal and inverse structures, (c) ligand-field stabilization energies (p. 1131) of cations on tetrahedral and octahedral sites, and (d) polarization or covalency effects. ... 

Ligand-Field Stabilization Energies 8.2.3 Contributions to the Chelate Effect - The Entropy... 

The ligand field stabilization energy is only one aspect of the formation of a transition state. Because the reactions are carried out in solutions, solvation of the transition state and the entering ligand may have enough effect to assist in the formation of a particular transition state. Also, the fact that some... 

Labile species are usually main group metal ions with the exception of Cr2+ and Cu2+, whose lability can be ascribed to Jahn-Teller effects. Transition metals of classes II and III are species with small ligand field stabilization energies, whereas the inert species have high ligand field stabilization energies (LFSE). Examples include Cr3+ (3d3) and Co3+ (3d6). Jahn-Teller effects and LFSE are discussed in Section 1.6. Table 1.9 reports rate constant values for some aqueous solvent exchange reactions.8... 

Many spinel compounds adopt an alternative structure where half the B cations occupy the tetrahedral sites while the remaining B cations and A cations occupy the octahedral sites. These are known as inverse spinels. The occupancy of the latter sites may be random or ordered. The adoption of an inverse spinel versus a spinel structure depends on a variety of factors the relative size of the A and B cations, the relative lattice energies, ligand-field stabilization, energies of octahedral versus tetrahedral coordination, and polarization or covalency effects. For example, in MgABOq one might expect the small... 

Two contributions to this trend are (a) the general decrease in electropositive character resulting from increased effective nuclear charge (see Topic HI) and (b) ligand field stabilization energies (see Topic H2). which increase the stability of complexes with ligands higher in the spectrochemical series than water in all ions except Mn (dr) and Zn (d ). 

Fig. 20.26 Ligand field stabilization energies as a function of for high-spin octahedral systems and for tetrahedral systems Jahn-Teller effects for and configurations have been ignored.

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