Ligand valence theory

An X-ray atomic orbital (XAO) [77] method has also been adopted to refine electronic states directly. The method is applicable mainly to analyse the electron-density distribution in ionic solids of transition or rare earth metals, given that it is based on an atomic orbital assumption, neglecting molecular orbitals. The expansion coefficients of each atomic orbital are calculated with a perturbation theory and the coefficients of each orbital are refined to fit the observed structure factors keeping the orthonormal relationships among them. This model is somewhat similar to the valence orbital model (VOM), earlier introduced by Figgis et al. [78] to study transition metal complexes, within the Ligand field theory approach. The VOM could be applied in such complexes, within the assumption that the metal and the... 

In some respects the ligand field theory is closely related, at least qualitatively, to the valence-bond theory described in the preceding sections, and many arguments about the structure of the normal state of a complex or crystal can be carried out in either of the two ways, with essentially the same results.66... 

The compound [Co(NH3)6]Cl3 is yellow-orange, whereas [Co(H20)3F3] is blue. Explain why these materials are so different using the valence bond and ligand field theories. 

The solid state properties of the linear chain compounds are substantially determined by the electronic structure of the molecular [Pt(CN)4]2 units. An ab initio calculation of the electronic structure of the [Pt(CN)4]2 complex including all 132 electrons or at least the 48 valence electrons does not exist as yet. Concerning the optical spectroscopy, however, mainly the highest occupied (HOMO) and the lowest unoccupied (LUMO) molecular orbitals are of interest. Thus, the number of electrons and states, which have to be considered, is restricted drastically compared to the full problem. The method usually applied to the approximative determination of the relevant states and their electronic structures is the molecular-orbital ligand field theory mostly using empirical fitting data50,31). 

The content of this book, which encompasses the chemistry of all of the chemical elements and their compounds, including interpretative discussion in the light of the latest advances in structural chemistry, general valence theory, and, particularly, ligand field theory, provides a reasonable achievement for students at the B.Sc. honors level in British universities and at the senior year graduate level in American universities Our experience is that a course of about eighty lectures is desirable as a guide to the study of this material. 

The CF picture gives a useful understanding of coordination chemistry and one that is widely used for qualitative discussions. A more sophisticated version of this approach, LF theory see Ligand Field Theory Spectra), which is really a conventional molecular orbital (or MO) picture, can be used for more accurate electronic structure calculations. In the CF model (Figure 5) we consider the s, the three p, and the five d orbitals of the valence shell of the isolated ion as well... 

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