Test: Coordination Chemistry- 2 - Chemistry MCQ

The correct answer is one Mn²⁺ and two Mn³⁺. The number of manganese ions in tetrahedral and octahedral sites, respectively in Mn₃O₄ are one Mn²⁺ and two Mn³⁺. Mn₃O₄ is composed of two Mn²⁺ ions at the A site and two Mn³⁺ ions at the B1 and B2 sites.

The spinels have the general chemical formula AB₂X₄. 

    Where:

    A^II = a divalent cation like Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn 

    B^III = a trivalent cation like Al, Ga, In, Ti, V, Cr, Mn, Fe, Fe, Co, Ni 

    X = O, S, Se etc.

Examples of Normal Spinels: MgAl₂O₄ (known as spinel), Mn₃O₄, ZnFe₂O₄, FeCr₂O₄ (chromite) etc.

Correct Answer :- d

Explanation : [Cr(H₂O)₆]³⁺ shows the strongest distortion from the regular octahedral structure.

The central Cr atom in +2 oxidation state has d⁷ outer electronic configuration. It has degenerate electronic states occupying the eg orbital set and tend to show stronger Jahn-Teller effects.

Correct Answer :- D

Explanation : The general trend of increasing electronegativity of the element when moving from left to right ia any horizontal row. The electronegativity increases due to which charge separation and ionization of hydrides increases.This increases the acidic strength of hydrides. 

The correct order is :

Ca²⁺, Mn²⁺, Fe³⁺, Cu²⁺

Spin Crossover Behavior

The complex [Fe(phen)2(NCS)2] (phen = 1,10–phenanthroline) exhibits spin crossover behavior. Spin crossover refers to the phenomenon where a compound undergoes a change in its spin state upon variation in temperature, pressure, or other external stimuli. In this case, the complex undergoes a change in its spin state as the temperature is changed.

CFSE and µeff at 250 K

At a temperature of 250 K, the complex has a certain crystal field splitting energy (CFSE) and an effective magnetic moment (µeff). The CFSE is a measure of the energy difference between the d orbitals in the presence of a ligand field. The µeff, on the other hand, is a measure of the magnetic moment of the complex.

CFSE and µeff at 150 K

At a temperature of 150 K, the complex exhibits a different CFSE and µeff compared to the values at 250 K.

Options and their CFSE and µeff values

Let's analyze the given options and their corresponding CFSE and µeff values at 250 K and 150 K:

A: 0.4 ∆o, 4.90 BM (250 K) and 2.4 ∆o, 0.00 BM (150 K)
B: 2.4 ∆o, 2.90 BM (250 K) and 0.4 ∆o, 1.77 BM (150 K)
C: 2.4 ∆o, 0.00 BM (250 K) and 0.4 ∆o, 4.90 BM (150 K)
D: 1.2 ∆o, 4.90 BM (250 K) and 2.4 ∆o, 0.00 BM (150 K)

Analysis and Conclusion

Comparing the given options with the provided CFSE and µeff values, we can determine that Option A matches the given values accurately. Therefore, the correct answer is Option A: 0.4 ∆o, 4.90 BM (250 K) and 2.4 ∆o, 0.00 BM (150 K).

This means that at 250 K, the complex has a CFSE of 0.4 ∆o and a µeff of 4.90 BM, while at 150 K, the CFSE is 2.4 ∆o and the µeff is 0.00 BM.

Please note that the CFSE and µeff values are specific to the complex [Fe(phen)2(NCS)2] and its spin crossover behavior at the given temperatures.

Electronic Configurations with Orbital Angular Momentum Contribution in Octahedral Environment

In an octahedral environment, the d-orbitals split into two sets of different energies due to the crystal field effect. The lower energy set, called the t²g set, consists of three orbitals (dxy, dyz, and dxz), while the higher energy set, called the eg set, consists of two orbitals (dx²-y² and dz²).

The electronic configurations that have orbital angular momentum contribution in an octahedral environment are d¹ and d². Let's understand why:

A. d¹ and high spin d⁴:
- In an octahedral environment, a d¹ configuration means that only one electron occupies the t²g set.
- The electron occupies one of the three t²g orbitals (dxy, dyz, or dxz).
- Since there is only one electron, there is no orbital angular momentum contribution.

B. d¹ and d²:
- In an octahedral environment, a d² configuration means that two electrons occupy the t²g set.
- The two electrons can occupy any two of the three t²g orbitals (dxy, dyz, or dxz).
- The presence of two electrons in the t²g set introduces orbital angular momentum contribution.
- The two electrons have opposite spins, resulting in a net orbital angular momentum.

C. d² and high spin d⁵:
- In an octahedral environment, a d² configuration means that two electrons occupy the t²g set.
- The two electrons can occupy any two of the three t²g orbitals (dxy, dyz, or dxz).
- The presence of two electrons in the t²g set introduces orbital angular momentum contribution.
- The two electrons have opposite spins, resulting in a net orbital angular momentum.
- A d⁵ configuration means that five electrons occupy the t²g and eg sets.
- The five electrons can occupy any combination of the t²g and eg orbitals.
- However, the presence of five electrons in the d orbitals does not introduce additional orbital angular momentum contribution.

D. high spin d⁴ and high spin d⁶:
- A high spin d⁴ configuration means that four electrons occupy the t²g and eg sets.
- The four electrons can occupy any combination of the t²g and eg orbitals.
- However, the presence of four electrons in the d orbitals does not introduce additional orbital angular momentum contribution.
- Similarly, a high spin d⁶ configuration means that six electrons occupy the t²g and eg sets, but it also does not introduce additional orbital angular momentum contribution.

Therefore, the only electronic configurations that have orbital angular momentum contribution in an octahedral environment are d¹ and d², making option B the correct answer.

Explanation:

The colour of potassium dichromate is due to Ligand to metal charge transfer.

- Potassium dichromate (K2Cr2O7) is an inorganic compound that contains the dichromate ion (Cr2O7 2-) as a ligand and potassium ions (K+) as the metal.
- When light interacts with a compound, it can be absorbed by the electrons present in the compound's atoms or ions.
- In the case of potassium dichromate, the dichromate ion (Cr2O7 2-) acts as a ligand and donates a pair of electrons to the central chromium ion (Cr).
- The dichromate ion has a deep orange color due to the presence of multiple double bonds between the oxygen and chromium atoms.
- When light passes through potassium dichromate, the electrons in the oxygen atoms of the dichromate ion absorb certain wavelengths of light.
- These absorbed wavelengths correspond to the complementary color of orange, which is blue.
- As a result, the transmitted light appears blue, giving potassium dichromate its characteristic color.

To summarize:

- The colour of potassium dichromate is due to ligand to metal charge transfer.
- The dichromate ion acts as a ligand and donates electrons to the central chromium ion.
- The absorption of specific wavelengths of light by the ligand-metal complex leads to the observed color of potassium dichromate.