Question 1

According to crystal field theory, why does the $$[\mathrm{Mn(H_2O)_6}]^{2+}$$ ion have 5 unpaired electrons, while the $$[\mathrm{Mn(CN)_6}]^{4-}$$ ion has only one unpaired electron?

Accepted Answer

Because $$\mathrm{H_2O} is a $$weak field ligand, causing a small crystal field splitting ($$\Delta$$), resulting in a high-spin complex with maximum unpaired electrons.

Question 2

Which of the following best describes the effect of a strong field ligand like $$\mathrm{CN^-} on $$the d-orbital splitting in an octahedral complex?

Accepted Answer

It increases the crystal field splitting energy ($$\Delta_{oct}$$), favoring electron pairing in the lower energy $$t_{2g}$$ orbitals.

Question 3

Show that the ground state, free ion, Russell-Saunders term for any half-filled orbital set must be an S term. Which of the following is the correct explanation?

Accepted Answer

For a half-filled shell, the maximum multiplicity is achieved when all electrons are unpaired and parallel, resulting in $$L = 0$$ and an S term.

Question 4

Which of the following is the ground state term symbol for a $$d^5$$ free ion according to Hund's rules?

Accepted Answer

$$^6S$$

Question 5

Consider the complex $$[\mathrm{Fe(CN)_6}]^{4-}. $$What is the electron configuration of the central metal ion?

Accepted Answer

[Ar] $$3d^6$$

Question 6

Which transitions are possible for $$[\mathrm{Fe(CN)_6}]^{4-}$$ and $$[\mathrm{Fe(H_2O)_6}]^{2+}$$ complexes in the visible region?

Accepted Answer

d-d transitions, but $$[\mathrm{Fe(CN)_6}]^{4-} is $$expected to be colorless due to a lack of unpaired electrons.

Question 7

If $$[\mathrm{Fe(CN)_6}]^{4-}$$ loses a cyanide ligand to generate a five-coordinated complex, what change in the crystal field splitting parameter ($$\Delta) $$would you expect?

Accepted Answer

$$\Delta$$ would decrease due to the lower coordination number and weaker field.

Question 8

Using the Tanabe-Sugano diagram, why is $$[\mathrm{Fe(CN)_6}]^{3-}$$ colorless?

Accepted Answer

Because all electrons are paired in the $$t_{2g}$$ orbitals, so no d-d transitions are possible.

Question 9

Which of the following best describes the difference between high-spin and low-spin octahedral complexes?

Accepted Answer

High-spin complexes have more unpaired electrons due to weak field ligands, while low-spin complexes have fewer unpaired electrons due to strong field ligands.

Question 10

Which of the following is a correct statement about the Russell-Saunders coupling scheme?

Accepted Answer

It is used to determine the ground state term symbol for atoms and ions with partially filled shells.

Question 11

A $$d^6$$ metal ion in an octahedral field with strong field ligands will have which electron configuration?

Accepted Answer

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

Question 12

Which of the following best explains why $$[\mathrm{Fe(H_2O)_6}]^{2+} is $$colored?

Accepted Answer

It has unpaired electrons that allow d-d transitions in the visible region.

Question 13

Which of the following is the correct ground state term for a $$d^5$$ ion according to the Russell-Saunders coupling scheme?

Accepted Answer

$$^6S$$

Question 14

Which of the following statements about the Tanabe-Sugano diagram is correct?

Accepted Answer

It is used to predict the electronic transitions and colors of transition metal complexes.

Question 15

Which of the following is a consequence of the pairing energy being greater than the crystal field splitting energy ($$\Delta) in an $$octahedral complex?

Accepted Answer

The complex will be high-spin with maximum unpaired electrons.

Crystal Field Theory, Russell-Saunders Terms, and Tanabe-Sugano Diagrams in Transition Metal Complexes

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