Question 1

Which of the following best explains why [Fe(H2O)6]Cl2 is paramagnetic while K4[Fe(CN)6] is diamagnetic, according to crystal field theory?

Accepted Answer

Because H2O is a weak field ligand, resulting in a high spin complex with unpaired electrons, while CN- is a strong field ligand, resulting in a low spin complex with all electrons paired.

Question 2

Calculate the crystal field stabilization energy (CFSE) for a high-spin d4 octahedral complex.

Accepted Answer

$$\mathrm{CFSE} = -0.6\Delta_{oct}$$

Question 3

Which of the following ligands would most likely produce a low-spin octahedral complex with Fe3+?

Accepted Answer

CN-

Question 4

For a d5 metal ion in an octahedral field, what is the CFSE for the low-spin configuration?

Accepted Answer

$$\mathrm{CFSE} = -2.0\Delta_{oct} + 2P$$

Question 5

Why are low-spin tetrahedral complexes very rare?

Accepted Answer

Because $$\Delta_{tet} is $$much smaller than $$\Delta_{oct}$$, so it is rarely greater than the pairing energy P.

Question 6

A complex [MBr4]- is found to have the maximum number of unpaired electrons among first-row transition metals. Which metal is most likely M?

Accepted Answer

Mn2+ (d5)

Question 7

Which experimental technique is most suitable for detecting unpaired electrons in a transition metal complex?

Accepted Answer

Electron Spin Resonance (ESR) spectroscopy

Question 8

What is the electronic configuration for a low-spin d6 octahedral complex?

Accepted Answer

$$t_{2g}^6 e_g^0$

Question 9

Which of the following statements about the Jahn-Teller effect is correct?

Accepted Answer

It states that any non-linear molecule in a degenerate electronic state will distort to remove the degeneracy.

Question 10

A square planar complex is most likely to be formed by which d electron count?

Accepted Answer

d8

Question 11

Which of the following best describes the effect of increasing ligand field strength on the spin state of an octahedral complex?

Accepted Answer

It favors the formation of low-spin complexes.

Question 12

Calculate the number of unpaired electrons in [Fe(CN)6]4-.

Accepted Answer

0

Question 13

Which of the following is a correct CFSE expression for a high-spin d7 octahedral complex?

Accepted Answer

$$\mathrm{CFSE} = -0.8\Delta_{oct}$$

Question 14

Which geometry is most likely to exhibit a tetragonal distortion due to the Jahn-Teller effect for a d9 metal ion?

Accepted Answer

Octahedral

Question 15

For a d3 octahedral complex, what is the expected spin state and CFSE?

Accepted Answer

Only one spin state, $$\mathrm{CFSE} = -1.2\Delta_{oct}$$

Question 16

Which of the following best explains why there are only two possible spin state configurations for d5 octahedral complexes?

Accepted Answer

Because $$\Delta_{oct}$$ can never equal P.

Question 17

Which of the following complexes is most likely to be diamagnetic?

Accepted Answer

[Fe(CN)6]4-

Question 18

What is the main factor that determines whether an octahedral complex will be high spin or low spin?

Accepted Answer

The relative magnitudes of $$\Delta_{oct}$$ and the pairing energy P

Question 19

Which of the following best describes the orbital splitting in a square planar complex compared to an octahedral complex?

Accepted Answer

The $$d_{x^2$-y^2$$}$ orbital is raised much higher in energy than the other d orbitals.

Crystal Field Theory: Spin States, Ligand Field Strength, and Applications

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