Crystal Field splitting energy

Question 1

What is crystal field theory?

Answer 1

An ionic model that considers ligands as point negative charges. It considers how the ligand field affects the energy of d orbitals

Question 2

What orbitals are destabilised by octahedral ligand fields and by how much?

Answer 2

Orbitals that are on the same axis the ligands approach, the eg orbitals (dz2,dx2-y2)
Destabilised by 0.6

Question 3

What orbitals are stabilised by octahedral ligand fields and by how much?

Answer 3

the orbitals that point between the ligand fields, the t2g orbitals (dx, dxz, dyz)
Stabilised by -0.4

Question 4

How much smaller is the splitting of tetrahedral ligand fields compared to octahedral fields?

Answer 4

4/9.

So to convert delta tet to delta oct, multiply delta tet answer by 4/9

Question 5

What orbitals are stabilised by tetrahedral ligand fields?

Answer 5

the e orbitals stabilised *dz2, dx2-dy2)

Stabilised by -0.6

Question 6

What orbitals are destabilised by tetrahedral ligand fields?

Answer 6

the t2 orbitals destabilised (dx2, dxz, dyz) by 0.4

Question 7

What is CFSE?

Answer 7

The energy difference between electron config in the crystal field and in the spherical ligand field

Question 8

What is the pairing energy?

Answer 8

The energy it takes to pair electrons in the same orbital.

This does not include pairs that would have been paired in a spherical ligand field.

Question 9

What is a spinel?

Answer 9

A crystal structure with general formula A(II)B(III)2O4

Contains tetrahedral and twice as many octahedral holes.

Question 10

How is a normal spinel arranged?

Answer 10

the A2+ ions in the tetrahedral holes and the B3+ ions in octahedral holes

Question 11

How is an inverse spinel arranged?

Answer 11

the A2+ ions occupy half the octahedral holes.

B3+ occupy the other half of octahedral holes and all tetrahedral holes

Question 12

What factors affect the size of crystal field splitting? (4)

Answer 12

1) nature of metal
2) nature of ligand
3) oxidation state of metal
4) geometry of complex

Question 13

How does oxidation state of metal affect crystal field splitting?

Answer 13

The higher the ox state the larger the splitting

Bc larger positive charge on M means ligands pulled closer causing more repulsion.

Question 14

How does the geometry of a complex affect the crystal splitting?

Answer 14

Tetrahedral splitting is much smaller than octahedral. It is 4/9ths smaller

Question 15

How does the nature of the ligand affect the crystal field splitting?

Answer 15

depending on the ligands place in the spectrochemical series will determine its affect on splitting.
Weak field ligands= small splitting (more likely high spin)
Strong field ligands= big splitting (more likely low spin)

Question 16

How do strong field ligands affect crystal field splitting?

Answer 16

Cause a large splitting (more likely low spin)

Question 17

How do weak field ligands affect crystal field splitting?

Answer 17

Cause a small splitting (more likely high spin)

Question 18

Examples of weak field ligands?

Answer 18

I-, Br-, S2-, SCN-

Question 19

Examples of strong field ligands?

Answer 19

CO, CN- PR3

Question 20

How does the nature of the transition metal affect crystal splitting?

Answer 20

Splitting tends to increase down the groups as d orbitals get larger.

Question 21

How does spin affect ionic radii?

Answer 21

High spin ions tend to be larger, since eg orbitals are occupied, these are directed at ligands

Question 22

What is the Jahn-Teller theorem?

Answer 22

Distortion of the complex to remove degeneracy of orbitals to create a lower energy system.
Occurs with high spin d4, low spin d7 and d9

Question 23

What number of d electrons forms square planar compounds?

Answer 23

d8

Question 24

What geometry do d8 ligand-metal complexes usually take?

Answer 24

Square planar

Question 25

What do high spin d4, low spin d7 and d9 ligand-metal complexes have in common?

Answer 25

affected by Jahn-Teller theorem