Crystal field theory limitations

Adsorption of Ag on the surface of PdO is also an interesting option offered by colloidal oxide synthesis. Silver is a well-known promoter for the improvement of catalytic properties, primarily selectivity, in various reactions such as hydrogenation of polyunsaturated compounds." The more stable oxidation state of silver is -F1 Aquo soluble precursors are silver nitrate (halide precursors are aU insoluble), and some organics such as acetate or oxalate with limited solubility may also be used." Ag" " is a d ° ion and can easily form linear AgL2 type complexes according to crystal field theory. Nevertheless, even for a concentrated solution of AgNOs, Ag+ does not form aquo complexes." Although a solvation sphere surrounds the cation, no metal-water chemical bonds have been observed. 

Historically, crystal field theory was the first theoretical model (11, 86, 101, 123) used to explain d-d transition energies in metal complexes. Its usefulness is restricted to those complexes whose bonding is largely ionic, and its mqjor deficiency arises from its inability to account for charge transfer transitions. The iterative extended Hiickel and the ab initio, limited basis set, Hartree-Fock calculations are capable of de-... 

There are some cases, however, where with limited data, valid comparisons can be made between transition metals ions and other cations of similar charge and size. It is possible to interpret qualitatively trends in the geochemical distribution of transition metal ions by crystal field theory. 

Glasby, G. P. (1975) Limitations of crystal field theory applied to sedimentary systems. Geoderma, 13,363-7 [see McKenzie (1970)]. 

Presently, it will be a concern to review the basics of crystal field theory as a vehicle to understand the electronic features of transition metal atoms and ions in an octahedral environment. Thus is considered the limited basis of ten spinorbitals of the partially occupied atomic d-shell for the relevant transition metal. A particular choice of basis is made in order to obtain a convenient form for the spin-orbital interaction and to simplify the application of the point group symmetry. The e-type orbitals spin factors, a basis for the four-dimensional irreducible representation U. The Kramers pairs will be used ... 

Crystal field theory can deal with the observed splitting between the d-orbital sets increasing with increasing oxidation state of the central metal atom. Since the ionic radius of an ion decreases as ionic charge (which equates with oxidation state for a metal ion) increases, the surface charge density increases, metal-ligand bond distances (r) decrease and the splitting A 0 (which varies with r-5) increases. However, CFT has some obvious limitations, which led to development of alternate models. It cannot easily explain why A0... 

However, the valence bond theory approach to transition metals has severe limitations. It fails to account for the absorption spectra and magnetic properties of coordination compounds. These and other properties are more satisfactorily explained by crystal field theory or ligand field theory. 

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