Chapter 2 Multiple Choice Questions

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. The factors that determine the electronic energy levels in a lanthanoid complex are (in decreasing order of magnitude):

orbital-orbital > spin-spin > spin-orbit > crystal field correct incorrect

spin-spin > orbital-orbital > spin-orbit > crystal field correct incorrect

spin-spin > orbital-orbital > crystal field > spin-orbit correct incorrect

crystal field > spin-orbit > spin-spin > orbital-orbital correct incorrect

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. The ground-state term symbol for Tm³⁺ is:

³H₆ correct incorrect

⁶H_15/2 correct incorrect

⁵H₀ correct incorrect

⁵H₁₀ correct incorrect

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. Complexes of Eu³⁺ are paramagnetic at room temperature because:

The electron configuration of Eu²⁺ is 4f⁷. correct incorrect

Low-lying excited states are occupied. correct incorrect

The free-ion formula does not apply to Eu³⁺. correct incorrect

The electron configuration of Eu³⁺ is 4f⁶. correct incorrect

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. In an aqueous solution of Pr³⁺, the ³H₄ to ³P₂ transition occurs at 444 nm and the ³H₄ to ³P₁ transition occurs at 469 nm. At what wavelength does the ³H₄ to ³P₀ transition occur?

494 nm correct incorrect

481 nm correct incorrect

431 nm correct incorrect

591 nm correct incorrect

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. Aqueous solutions of Ce³⁺ appear colourless because:

The crystal field splitting is very small. correct incorrect

Electronic transitions occur in the IR and the UV. correct incorrect

f - f transitions are forbidden by the Laporte selection rule. correct incorrect

The molar extinction coefficient (e) is very small. correct incorrect

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. [Eu{bipy(2.2.2)}]³⁺ exhibits intense luminescence in aqueous solution when irradiated with UV radiation (bipy(2.2.2) is a neutral cryptand ligand that contains three 2,2-bipyridyl units).
Which of the following does not contribute to the intense luminescence?

There are no H₂O ligands so vibrational de-excitation is prevented. correct incorrect

bipy(2.2.2) has a high extinction coefficient for UV absorption. correct incorrect

Eu³⁺ is easily reduced to Eu²⁺ by excitation of the bipy(2.2.2) correct incorrect

The bipy(2.2.2) triplet state is higher in energy than the ⁵D₁ state of Eu³⁺. correct incorrect

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. Which of the following would not exhibit pseudocontact shifting in its NMR spectra at room temperature?

A low-symmetry Eu³⁺ (4f⁶) complex correct incorrect

A Pr³⁺ (4f²) complex with axial symmetry correct incorrect

A Pr³⁺ (4f²) complex with tetrahedral symmetry correct incorrect

A Tb³⁺ (4f⁸) complex with axial symmetry correct incorrect

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. Which of the following statements about the electronic absorption spectra of Pr³⁺ complexes is incorrect?

The absorptions are sharp. correct incorrect

For the ³H₄-³P₂ transition, e ˜ 1.5 M^-1 cm^-1. correct incorrect

The spectra are very sensitive to the identity of the ligands. correct incorrect

The spectra are insensitive to the coordination geometry. correct incorrect

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. Which of the following properties is not required (or at least desirable) in a lanthanoid single ion magnet?

Ligands in the equatorial plane of the complex correct incorrect

Axially symmetric crystal field correct incorrect

Anisotropic electron distribution correct incorrect

Large (by lanthanoid standards) crystal field splitting correct incorrect

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. When an aqueous solution of Tb³⁺ is irradiated with a UV lamp, there is no visible luminescence. Consider the following possible explanations:
(i) Direct excitation of Tb³⁺ is inefficient
(ii) [Tb(H₂O)_n]³⁺ is extremely labile
(iii) The emission from Tb³⁺ is in the IR
(iv) Tb³⁺ undergoes photochemical oxidation to Tb⁴⁺
(v) Luminescence is quenched by vibrational de-excitation
Now select the correct statement below.

(i), (ii) and (v) together are a correct explanation correct incorrect

(i) and (v) together are a correct explanation correct incorrect

(iii) is the correct explanation correct incorrect

(ii) and (iv) together are a correct explanation correct incorrect