JAHN- TELLAR EFFECT It was stated by Jahn and Teller that any non –linear molecular system in orbitally degenerate electronic state (i.e., a state which represents more than one electronic arrangement of the same energy) would be unstable and that it would get stabilised by undergoing distortion in its geometry and thus by causing a split in its orbitally degenerate electronic state. The above statement is known as Jahn-Tellar effect. The distortion in the geometry of the non-linear molecular system thus produced is known as Jahn-Tellar distortion. The lowering of symmetry of the non-linear system due to Jahn –Tellar effect always occurs in a manner which results in decrease in the energy of the system. Let us consider an octahedral complex of Cu +2 with unidentate ligands L - . The Cu +2 ion in a perfect octahedral ligand environment has the ground state electronic configuration t 6 2g e 3 g which represents two electronic arrangements t 6 2g d 2 z 2 d 1 x 2 -y 2 of equal ...

FACTORS AFFECTING THE CFS There are various factor which affect the value of CFS. Which are as follow with their description Oxidation state of the metals  Crystal field splitting increases on increasing in oxidation state of the metal. This is because the ligands with their electron density can approach the higher-charge (smaller sized) metal-ion more closely and interact more strongly with the d orbitals. Thus the complex [Co(NH 3 ) 6 ] + 3   in which Co in 3+ oxidation state has large crystal field splitting and [Co(NH 3 ) 6 ] 2 + with Co in 2+ oxidation state possesses small crystal field splitting . Principal Quantum no./ Size of the d orbital Crystal field splitting increases with increase in the principal quantum no. of the d- orbital. As the Principal Quantum number increases the distance of the d-orbital of the metal from its nucleus increases. Such an orbital interacts more strongly with the ligands giving large splitting. In genral, crystal fiel...

Crystal Field Splitting Energy we know that an electron always prefers to occupy an orbital of a lower energy level. It is evident that if an octahedral complex contain one d electron, that electron will reside in one of the t 2g orbitals. This orbital has an energy -4 Dq compared to the energy of the hypothetical degenerate orbitals of state II as shown in fig.. Thus, the complex will be 4 will be 4 Dq more stable than predicted by the pure electrostatic theory. Evidently, the energy of the complex would now be less the decrease in energy = 0- (- 4Dq) = 4Dq is called the Crystal Field Splitting Energy (CFSE) of the complex under consideration. So the CFSE can be defined as "The energy difference of the energy of orbital in which the d-block electron exist after splitting with the energy of the degenerated d orbitals."  Calculation of  CFSE for octahedral compound As above mentioned for the filling of first electron in the  t 2g is 4Dq. So for each electron...

Proposed by H. Bethe & Van Bleck(1935) H. Bethe  Van Bleck Used fo r  Firstly used for the   explanation of color and the magnetic properties of crystalline solid. In 1951, several theoretical chemists working independently used crystal field theory to interpret the spectra of transition metal complexes. Principle-  it is based on the principle of electrostatic theory, "the bond energy between two oppositely charged ions q and q' placed at a distance between 'r' with each other is given by the equation  Salient features of CFT The bond between the metal and the ligands is 100% ionic. In the coordination compound the charges are present in metal ions and ligands. Metal act as a positive charge whereas the negative charge is due to the ligands as the point charge in anion or the point dipole in the neutral ligands like water and ammonia. The interaction between the metal ion and ligands is attractive wh...

CRYSTAL FIELD SPLITTING   Before the study of this topic we have first know about the spatial orientation of d- orbitals. The five d orbitals can be designated as follow The first three orbital are oriented in between the XY, YZ, ZX axes respectively and these three orbital are called t 2g or d E  and the rest two orbitals are oriented along the XY and Z axes respectively and are known as e g  or d r. Now we will discuss about our topic which is  CRYSTAL FIELD SPLITTING,   in the absence of any ligands or in the case of free metal ion, all the five d-orbitals have the same energy and the orbitals having the  same energy are called degenerate orbitals. However in the approach of the ligands, the orbital electrons will be repelled by the lone pair (or negative charge) of the ligands. The repulsion will raise the energy of d - orbitals, the energy of each orbital will increase by the same amount, due to spherical field or s...