what are the limitations of crystal field theory?

Question

the question is about the chemistry of transition metal complexes

Answer 1

the most obvious limit of this theory is that it can't explain thee color of substances with a full or empty d orbital.(since it only consider d orbitals) an example of these substances is KMnO4 in which the d orbital is empty. there is another kind of electron transfer called Charge Transfer(CT) which is more powerful than d-d transfer and is between metal and ligand. this type of electron transfer is not covered in crystal field theory and can only be explained using MOT(molecular orbital theory)

Answer 2

Crystal Field Theory Pdf

Answer 3

Crystal field theory is used to describe the electronic structure of transition metal complexes. It is successful in describing the magnetic properties, colors, hydration enthalpies and spinel structures of transition metal complexes, but it cannot provide an adequate description of bonding. Crystal field theory was developed by the physicists Hans Bethe and John Hasbrouck van Vleck. It was combined with molecular orbital theory to form ligand field theory, which delivers insight into the process of chemical bonding in transition metal complexes.

In crystal field theory the metal ion is assumed to be free in gas form, the ligands are assumed to behave like point charges and it is assumed that the orbitals of the metal and the ligands do not interact. A refined form of crystal field theory called ligand field theory takes an empirical constant called the Racah parameter in the calculations to make up for covalent effects.

The bonding between a transition metal and the ligands is due to the attraction between the positively charged metal ion and the electrons of the ligand. Crystal field theory describes how the ligands pull on some of the 3d electrons and split them in to higher and lower (in terms of energy) groups. This crystal field splitting depends on several factors:

* the nature of the metal ion, specifically the number of electrons in the d orbitals
* the metal's oxidation state. A high oxidation state leads to high energy splitting.
* the arrangement of the ligands around the metal ion.
* the nature of the ligands surrounding the metal ion. The stronger the ligands then the greater the energy difference between the split high and low 3d groups, this is called spectrochemical series.

The most common type of complex are octahedral complexes; here six ligands form an octahedral field around the metal ion, the ligands point directly into the d-orbitals and cause high-energy splitting. Tetrahedral complexes are the second most common type; here four ligands form a tetrahedral field around the metal ion, since in this case the ligands' electrons aren't oriented directly against the d-orbitals the energy splitting will be lower than in the octahedral case. Square planar complexes are mostly by transition metals in period 5 and 6 and nickel in period 4. Crystal field theory works best for period 4 transition metals.

Answer 4

Crystal Field Theory is unable to explain the relative strength of ligands.In CFT pi orbitals of the ligands are not considered.CFT gave no information about pi bond formation in ligands.CFT ignores the attractive forces between d-electrons of metal ion and nuclear charge on ligand atom.Therefore all properties depend upon the ligand orbitals and their interactions with metal orbitals are not explained.CFT can not explain the colour of complexes with a full or empty d-orbitals because it only consider d-orbitals.

Answer 5

"An ionic theory which is an offshoot of electrostatic theory. It ignores all covalent bonding effects. It was developed by Hans Bethe in 1929 by applying group theory and quantum mechanics to electrostatic theory. It was further developed by physicists during the 1930s and 1940s. It can be used to predict chemical properties, kinetic properties, reaction mechanisms, magnetic and spectral properties, and thermodynamic data.
It cannot, however, be applied to sulfides, since sulfide forms mainly covalent bonds."

Unless I misunderstand your question, that final sentence is the answer you're looking for: the theory is limited in that it cannot be applied to sulfides.