Topic 9: Crystal Field Theory Part 2

elongation and compression

Any non-linear molecular system in a degenerate electronic state will be unstable and will distort to form a system of lower symmetry and lower energy, thereby removing the degeneracy

A set of orbitals that have the same energy leveL

z^2 increases in energy by 1/2 delta 1 x^2-y^2 decreases in energy by 1/2 delta 1 xz and yz increase in energy by 1/3 delta 2 xy decreases in energy by 2/3 delta 2

x^2-y^2 increases in energy by 1/2 delta 1 z^2 decreases in energy by 1/2 delta 1 xy increases in energy by 2/3 delta 2 xz and yz decrease in energy by 1/3 delta 2

delta O»_space; delta 1 > delta 2

eg they point at the ligands and are most affected by distortions

Whichever removes the degeneracy

x^2-y^2 increases in energy by »_space; z^2 decreases in energy by »_space; xy increases in energy by > xz and yz decrease in energy by > xy higher in energy than z^2 difference between x^2-y^2 and xy is delta SP

approximately equal

x^2-y^2 very high in energy

Very large delta 2nd and 3rd row transition metals have this (4d and 5d), d^8 configurations have SP e.g. Pd^2+ strong field ligands e.g. [Ni(CN4)]^2-

tetrahedral

4/9

general decrease left to right + additional decreases because of CFSE affects which are favoured by small bond differences. d^3, d^6 LS, d^8 HS