Key difference - crystal field theory vs. ligand field theory
Many scientists and chemists have tried to formulate theories to explain the binding of coordination compounds and to establish and predict their properties. The first successful theory is valence bond theory published by Linus Pauling in the 1930s. Then in 1929 Hans Bethe proposed a new theory called the crystal field theory. The ligand field theory is a modification of the original crystal field theory. In the beginning, the crystal and ligand field theories were mainly used to explain the concepts of solid state physics. However, in the 1950s, chemists began applying these theories to transition metal complexes. The main difference between crystal field theory and ligand field theory is that crystal field theory only describes the electrostatic interaction between metal ions and ligands, while ligand field theory takes into account both the electrostatic interaction and the covalent bond between the metal and its ligand .
This article explains
1. What is crystal field theory - theory, application 2. What is ligand field theory - theory, application 3. What is the difference between crystal field theory and ligand field theory
What is crystal field theory?
The crystal field theory describes the electronic structure of metal crystals, whereby they are surrounded by oxide ions or anions. The symmetry of the electrostatic field depends on the crystal structure. The d orbitals of the metal ions are split up by the electrostatic field and the energies of these d orbitals can be calculated as crystal field stabilization energies. Crystal field theory is used to understand the magnetic, thermodynamic, spectroscopic, and kinetic properties of coordination metal complexes. The three main assumptions of crystal field theory include:
(a) The ligands are considered to be point charges,
(b) No interaction / bonds between metal orbitals and ligands
(c) In a free metal ion, all subshells of a certain d orbital have the same energy.
The interactions between metal ions and their ligands are electrostatic in nature. No bond between the atom and the transition metal is considered in this theory. Due to this limitation, the crystal field theory is modified and proposed as ligand field theory.
What is ligand field theory?
The ligand field theory is a combination of crystal field and molecular orbital theories. It was first suggested qualitatively by Griffith and Orgel. Ligand field theory is used to describe the bonding, orbital arrangement, and other important properties of coordination metal complexes. In addition, it describes p-bonds and provides more accurate calculations of energy levels in relation to the stabilization energies of the ligand field. More specifically, ligand field theory is used to assess the electron distribution between the d orbitals of metal ions and their stereochemical activity. The description of covalent bonds is not found in crystal field theory. Therefore, ligand field theory is used as a more realistic model that can be used to describe the properties of coordination complexes.
Difference between crystal field theory and ligand field theory
Crystal field theory: The crystal field theory is a theory that describes the electronic structure of metal crystals.
Ligand field theory: The ligand field theory is a modification of the crystal field theory and the molecular orbital theory .
Crystal field theory: The crystal field theory describes only electrostatic interactions between metal ions and ligands
Ligand field theory: The ligand field theory describes both electrostatic interactions and covalent bonds between metal ions and ligands.
Crystal field theory: The crystal field theory only provides the electronic structure of transition metals.
Ligand field theory: Ligand field theory provides electronic, optical and binding properties of transition metals.
Crystal field theory: The crystal field theory is comparatively unrealistic
Ligand field theory: The ligand field theory is more realistic than the crystal field theory.
Summary - crystal field theory and ligand field theory
Crystal field theory is an electrostatic approach that describes the electronic energy levels that determine the UV-visible spectra, but does not describe any bond between metal ions and ligands. Ligand field theory is a complete description derived from crystal field theory. In contrast to crystal field theory, ligand field theory describes the bond between metal ions and ligands. This is the difference between crystal field theory and ligand field theory.
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