Crystal field energy development

When a metal ion is surrounded by anions in a crystal, there is an electrostatic field produced by the anions that alters the energies of the d orbitals of the metal ion. The field generated in this way is known as a crystal field. Crystal field theory was developed in 1929 by Hans Bethe in an attempt to explain the spectral characteristics of metal ions in crystals. It soon became obvious that anions surrounding a metal in a crystal gave a situation that is very similar to the ligands (many of which are... 

The above discussion has considered the stabilization of complexes in terms of the crystal field theory. It is desirable to consider the same topic in terms of modern molecular orbital theory. Although the development and sophisticated consideration of the MO treatment is far beyond the scope of this chapter, an abbreviated, qualitative picture will be presented, focusing again on the energy levels of the highest occupied and lowest empty orbitals and again using the square planar d case. 

We have estimated each of the parameters in Eq. (2) in a unified manner by combining the strengths of several previous molecular modeling studies. We used the force field of Karasawa and (ioddard" to model the atomic potential energy surface and to describe the charge distribution at the atomic level. This force field includes the effects of electronic polarization via the shell model of electronic polarization, originally developed by Dick and Overhauser." By direct minimization of total crystal free energy with respect to both the atomic and shell... 

The foregoing discussion of valence is. of course, a simplified one. From ihe development of the quantum theory and its application to the structure of the atom, there has ensued a quantum theory of valence and of the structure of the molecule, discussed in this hook under Molecule. Topics thal are basically important to modem views of molecular structure include, in addition to those already indicated the Schroedinger wave equation the molecular orbital method (introduced in the article on Molecule) as well as directed valence bonds bond energies, hybrid orbitals, the effect of Van der Waals forces and electron-dcticiem molecules. Some of these subjects are clearly beyond the space available in this book and its scope of treatment. Even more so is their use in interpretation of molecular structure. [However, sec Crystal Field Theory and Ligand.)... 

Develop a crystal field splitting diagram for the d orbitals of the metal in a trigonal bipyramidal complex [ML-] showing, qualitatively, how the energies of each of the d orbitals change. 

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