Ligand field theory, application symmetry

Warren KD (1984) Calculations of the Jahn-Teller Coupling Constants for d Systems in Octahedral Symmetry via the Angular Overlap Model. 57 119-145 Warren KD (1977) Ligand Field Theory off-Orbital Sandwich Complexes. 33 97-137 Warren KD (1976) Ligand Field Theory of Metal Sandwich Complexes. 27 45-159 Watson RE, Perlman ML (1975) X-Ray Photoelectron Spectroscopy. Application to Metals and Alloys. 24 83-132... 

Although the application of elementary ligand field theory is adequate to explain many properties of complexes, there are other factors that come into play in some cases. One of those cases involves complexes that have structures that are distorted from regular symmetry. Complexes of copper(II) are among the most common ones that exhibit such a distortion. 

Principles of symmetry and group theory find applications in several areas of quantum chemistry like chemical bonding, molecular spectroscopy, ligand field theory, crystal field theory etc. The procedure in all these cases involves—... 

Molecular symmetry and ways of specifying it with mathematical precision are important for several reasons. The most basic reason is that all molecular wave functions—those governing electron distribution as well as those for vibrations, nmr spectra, etc.—must conform, rigorously, to certain requirements based on the symmetry of the equilibrium nuclear framework of the molecule. When the symmetry is high these restrictions can be very severe. Thus, from a knowledge of symmetry alone it is often possible to reach useful qualitative conclusions about molecular electronic structure and to draw inferences from spectra as to molecular structures. The qualitative application of symmetry restrictions is most impressively illustrated by the crystal-field and ligand-field theories of the electronic structures of transition-metal complexes, as described in Chapter 20, and by numerous examples of the use of infrared and Raman spectra to deduce molecular symmetry. Illustrations of the latter occur throughout the book, but particularly with respect to some metal carbonyl compounds in Chapter 22. 

Recent applications of the ligand field theory to the transition metal complexes give logical interpretations of d-d absorption spectra, and the theoretical treatments help to predict band positions in the absorption spectra of complexes. On the other hand, today low-symmetry complexes are synthesized which contain ligands of more than three kinds. Their spectral data are expected to further develop theoretical fields of spectroscopy. 

Introduction to Ligand Field Theory, McGraw-HiU, New York, 1962. Important aspects of symmetry apphed to this topic can he found in F. A. Cotton, Chemical Applications of Group Theory, 3rd ed., Wiley InterScience, New York, 1990. An excellent review of photosensitizers can he found in T. Nyokong, V. Ahsen, eds.. Photosensitizers in Medicine, Environment, and Security, Springer, 2012. 

An inspection of the experimental data for normal paramagnets shows that deviations from the spin-only formula mostly towards higher values are frequently found. In fact, the amount to which the orbital contribution is quenched depends on the electron configuration and on the symmetry of the particular compound. The structural implications of these observations have been widely used in the past and the results are discussed in various magnetochemical publications [6, 25] and standard coordination chemistry textbooks. It has been found that, in general, the application of ligand field theory is often very useful in order to understand the magnetic behaviour of transition metal complexes. In this respect, we refer to the texts listed in the reference section I.I.8.2. 

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