Crystal field theory spectrochemical series

The spectrochemical series was established from experimental measurements. The ranking of ligands cannot be fully rationalized using crystal field theory, and more advanced bonding theories are beyond the scope of general chemistry. 

Pi bonding between metal and ligands provides a simple raison d etre lor strong field ligands, an issue that crystal field theory could not resolve. If we examine the strong field end of the spectrochemical series (page 405), we find ligands such as nitrite ion, cyanide ion, carbon monoxide, phosphites, and phosphines. The latter two owe their positions in the series to their ability to serve as rt acceptors, as described above, which increases the value of A, relative to what it would be in u [Pg.756]

Such an order is difficult to rationalize in terms of electrostatic energies embodied in the simple point-charge model of crystal field theory. For example, the charged O2- anion precedes the dipolar H20 molecule in the spectrochemical series. Note that the spectrochemical series differs from the nephelauxetic series discussed in chapter 11 (eq. 11.6), which is a measure of the degree of covalent bonding. 

The failure of crystal field theory and VB theory to explain the spectrochemical series stimulated the development of ligand field theory, which applies qualitative methods of molecular orbital theory to describe the bonding and structure of coordination complexes. The terms ligand field theory and molecular orbital theory are often used interchangeably in inorganic chemistry today. 

Crystal field theory does not account for the strengths of ligands revealed by the spectrochemical series. 

Crystal Field Theory 25-9 Color and the Spectrochemical Series... 

Spectrochemical series are empirical generalizations and simple crystal field theory cannot account for the magnitudes of Aoct values. 

Describe the crystal field theory of bonding in coordination compounds Explain the origin of color in complex species Use the spectrochemical series to explain colors of a series of complexes... 

When these lists of ligands are combined, the result is the spectrochemical series (which is actually older than crystal field theory ), which runs roughly in order from strong 77-acceptor ligands to strong rr-donor ligands ... 

Spectrochemical Studies. In the newly established laboratory Tsuchida began to measure quantitatively the absorption spectra of cobalt complexes, first by remeasuring the absorption spectra reported by Shibata and then preparing new complexes with various ligands. The results were summarized in the shift rules of absorption bands with the replacement of ligands, i.e., the spectrochemical series, which was reported first in 1938 (45) and was refined in 1955 (46). Its importance was recognized after World War II by its relation to the crystal field theory. In this field of research important works of physicists such as Yukito Tanabe and Satoru Sugano after the war deserve mention (47). 

Isomerism in Coordination Compounds 25-6 Structurai (Constitutionai) isomers 25-7 Stereoisomers Bonding in Coordination Compounds 25-8 Crystal Field Theory 25-9 Color and the Spectrochemical Series... 

Briefly describe the crystal field theory. Define the following terms crystal field splitting, high-spin complex, low-spin complex, spectrochemical series. 

Briefly describe each of the following ideas, phenomena, or methods (a) spectrochemical series (b) crystal field theory (c) optical isomer (d) structural isomerism. 

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