JAHN-TELLER EFFECT : JAHN-TELLER EFFECT Introduction, theorem, tetragonal distortion INTRODUCTION : INTRODUCTION In 1937 Jahn and Teller put forward a theorem known as Jahn –Teller theorem.
This explain why certain 6 coordinated complexes undergo distortion to assume distorted octahedral (i.e. tetragonal) geometry. REGULAR OCTAHEDRAL COMPLEXES : REGULAR OCTAHEDRAL COMPLEXES The 6 coordinated complexes in which all the 6 distances between the ligand and metal are equal are said to be regular /symmetrical octahedral complexes DISTORTED OCTAHEDRAL COMPLEXES : DISTORTED OCTAHEDRAL COMPLEXES The 6 coordinated complexes in which all the 6 distances between the ligand and metal are not equal are said to be distorted octahedral complexes JAHN TELLER THEOREM : JAHN TELLER THEOREM Any non liner molecular system possessing degenerated electronic state will be unstable and will undergo distortion to form a system of lower symmetry and lower energy and thus will remove degeneracy Z-OUT DISTORTION : Z-OUT DISTORTION Z-IN DISTORTION : Z-IN DISTORTION SYMMETRICAL AND UNSYMMETRICAL t2g : SYMMETRICAL AND UNSYMMETRICAL t2g The symmetrical t2g orbitals are t2g0, t2g3, t2g6
The unsymmetrical t2g orbitals are t2g 1,t2g 2,t2g4, t2g5 SYMMETRICAL AND UNSYMMETRICAL eg ORBITALS : SYMMETRICAL AND UNSYMMETRICAL eg ORBITALS The symmetrical eg orbitals are eg0, eg4,
The unsymmetrical eg orbitals are eg1, eg3
The eg2 orbital is symmetrical when configuration is (dx2-y2)1(dz2)1and unsymmetrical when configuration is (dx2-y2)0(dz2)2 Slide 11: t2g(sym)+eg(sym)=No Distortion