CH611 - Crystal Field Theory

Question 1

Answer 1

Question 2

Answer 2

Question 3

Answer 3

Question 4

Answer 4

Question 5

Answer 5

Question 6

Answer 6

Question 7

Answer 7

Question 8

Answer 8

Correction: Δ_T < Δ_o due to reduced number of ligands (4 in Td vs 6 in Oh).

Question 9

Answer 9

Note: Jahn-Teller effect can also occur, albeit to a lesser degree, because of non-uniform electron configurations in degenerated nonbonding orbitals (e.g a high-spin d⁷ configuration in an octahedral field).

Question 10

Weak field ligands are π ____, while strong field ligands are π ____.

Answer 10

π donors (π bases)
π acceptors (π acids)

Question 11

H₂O is a weak ____ because it has a ____ in an ____ orbital.

It is lower than NH₃ in the spectrochemical series.

Answer 11

H₂O is a weak π donor because it has a lone pair in an unhybridized p orbital.

Question 12

S(CH₃)₂ is a weak ____ because it has a ____ in an ____ orbital.

Answer 12

S(CH₃)₂ is a weak π donor because it has a lone pair in an unhybridized p orbital.

Similar bonding mechanism as water.

Question 13

PPh₃ is a fairly strong ____ because it has empty ____ orbitals on the ____ atom.

Answer 13

π acceptor (π acid)
d
P

Question 14

P(Et)₃ is a ____ because it has empty ____ orbitals on the ____ atom.

Answer 14

π acceptor (π acid)
d
P

Question 15

N-bonded NO₂ is a ____.

Answer 15

σ base

Question 16

O-bonded NO₂ is a ____.

Answer 16

π donor or an ambiguous ligand (depends on the bonding oxygen).

Question 17

CN^- and CO are ____ ligands.

Answer 17

Strong field ligands (large
Δ_O).

Question 18

Rank the following by Δ_O:

SCN, NCS

Answer 18

Δ_O(NCS) > Δ_O(SCN)

SCN is a π donor while NCS is a π acceptor

Question 19

Δ_O(Fe³⁺) is ____ than Δ_O(Fe²⁺) because of its ____.

Answer 19

greater than
higher oxidation state

Higher oxidation state = smaller ionic radii = stronger metal-ligand interaction

Question 20

4d and 5d metals (or any metal in lower d-block period) are generally ____ splitting.

Answer 20

Strong splitting (larger Δ_O)

As with Ru³⁺ vs Fe³⁺.

Larger primary quantum number (n) = larger orbitals on metal atom = stronger metal-ligand interaction.

Question 21

The electron configuration of a metal atom in a ____-spin complex is similar to that of a ____ atom.

Answer 21

High-spin
Free ( atom in a spherical field)

Question 22

In a diamagnetic material, all electrons are ____.
A diamagnetic material is ____ by an external magnetic field.

Answer 22

Paired
Slightly repelled

Question 23

A paramagnetic material has ____.
Paramagnetic materials are ____ an external magnetic field.

Answer 23

Unpaired electrons
Drawn toward

Question 24

Materials with a larger measured magnetic dipole moment (μ) are more ____.

Answer 24

Paramagnetic

Question 25

The source of magnetic moment μ in paramagnetic coordination compounds is \_\_\_\_.

Answer 25

Electronic spin (spin-only paramagnetism). Atoms\ions that are part of a complex usually have quenched orbital angular momentums.

Question 26

Given the number of unpaired electrons N, the spin-only magnetic moment μ is:

Answer 26

## Footnote μ_B - Bohr magneton

Question 27

Given the total spin quantum number S, the spin-only magnetic moment μ is:

Answer 27

## Footnote μ_B - Bohr magneton

Question 28

The total spin quantum number S for an atom with N unpaired electrons is:

Answer 28

S=1/2 N ## Footnote Each unpaired electron contrinites a spin of 1/2.

Question 29

Tetrahedral complexes are always HS, because \_\_\_\_ is smaller than \_\_\_\_.

Answer 29

Δ_T P ## Footnote P - Pairing energy

Question 30

Explain the Jahn-Teller Effect.

Answer 30

If the ground electronic configuration of a nonlinear complex (T_d or O_h) is orbitally degenerate, and asymmetrically filled, then the complex distorts so as to remove the degeneracy and achieve a lower energy.

Question 31

Manifestation of Jahn-Teller effect in Octahedral complexes?

Answer 31

In an O_h complex, this effect manifests as a tetragonal distortion (elongation\compression along mutually perpendicular axes).

Question 32

compared to \_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_\_ is a more common form of tetragonal distortion since \_\_\_\_ instead of \_\_\_\_ bonds are weakened.

Answer 32

Equatorial Elongation Axial Elongation 2 4