Topic 9: Crystal Field Theory Part 2

Question 1

The 2 types of distortion are …

Answer 1

elongation and compression

Question 2

Jahn-Teller Theorem

Answer 2

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

Question 3

degenerate orbitals

Answer 3

A set of orbitals that have the same energy leveL

Question 4

How is an octahedral CFSE diagram affected by by compression tetragonal distortion.

Answer 4

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

Question 5

How is an octahedral CFSE diagram affected by by elongation tetragonal distortion.

Answer 5

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

Question 6

order of magnitude of delta 1, delta 2 and delta O

Answer 6

delta O&raquo_space; delta 1 > delta 2

Question 7

distortions are generally more pronounced if the degeneracy occurs in the … orbital because …

Answer 7

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

Question 8

How can you tell if the distortion will be an elongation or a compression?

Answer 8

Whichever removes the degeneracy

Question 9

How is a square planar CFSE diagram affected by by elongation tetragonal distortion.

Answer 9

x^2-y^2 increases in energy by &raquo_space;
z^2 decreases in energy by &raquo_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

Question 10

delta SP is … delta O

Answer 10

approximately equal

Question 11

In an SP CFSE diagram, electrons avoid the … orbitals because …

Answer 11

x^2-y^2
very high in energy

Question 12

What drives a square planar arrangement?
What can cause this?

Answer 12

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-

Question 13

Is tetrahedral or square planar more common?

Answer 13

tetrahedral

Question 14

delta T = … delta O

Answer 14

4/9

Question 15

Trend in ionic radii for octahedral M^2+ complexes

Minima at …

Answer 15

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