Tetragonal and Jahn-Teller Distortions

Question 1

How many d electrons does Cu2+ have

Answer 1

1. 9

Question 2

What 6-coordinate structures do Cu2+ complexes form

Answer 2

1. Lengthened axial bond distances

2. Departure from ideal octahedral symmetry- tetragonal distortion

Question 3

What is tetragonal distortion an example of

Answer 3

1. The Jahn-Teller effect

Question 4

Define the Jahn-Teller effect

Answer 4

1. If the ground state electronic configuration of a non-linear molecule is orbitally degenerate, then the molecule will distort so as to remove the degeneracy and achieve a lower energy

Question 5

What does orbital degeneracy mean

Answer 5

1. more than 1 electronic configuration possible, all with equal energy

Question 6

Why does Cu2+ show orbital degeneracy

Answer 6

1. Has 9 d electrons
2. 3 electrons to place in the two 3g orbitals
3. Two possible electronic arrangements, both of equal energy

Question 7

What happens to the splitting in a Cu2+ complex

Answer 7

1. z components are stabilised
2. Without z are destabilised
3. dx^2-y^2 goes to top
4. Then dz^2
5. Then dxy
6. then dxz, dyz

Question 8

Why does tetragonal distortion occur

Answer 8

1. A tetragonal distortion towards a square planar geometry, with the electron pair in the dz^2 orbital results in the 2 eg orbitals having different energies and the energy of the resulting complex is lower than the undistorted complex
2. M-L extension along the z-axis and an M-L compression along the x- and y-axis
3. Overall 2 electrons are stabilised and 1 electron is destabilised
4. Lowering overall energy

Question 9

How much lower is the J-T distorted complex compared to the undistorted

Answer 9

1. Total energy of electrons is lower in J-T distortion complex configuration by an amount DE

Question 10

What other electronic configurations does J-T effect occur in

Answer 10

1. d1, d2, d4, d6,d7

Question 11

When does degeneracy removal happen

Answer 11

1. It is viewed as occurring after the electrons enter the orbitals in the crystal field
2. J-T distortion doesn’t alter the way the electrons fill the orbitals.

Question 12

Where have the biggest Jahn-Teller effects been noted

Answer 12

1. for ground-state electronic configurations that have degeneracy in eg orbital occupancy
2. As they point directly at incoming ligands so feel repulsion more than in t2g

Question 13

Why is there a small bump after the lambda max in spectra for [Ti(OH2)6]3+

Answer 13

1. Tetragonal distortion means the electron can be promoted to either dz^2 or dx^2-y^2
2. Both transitions are close in energy
3. Therefore, one appears on a shoulder of the other