The calculated and observed magnetic moments differ considerably for an aqua complex of a Lanthanide (III)… · ABC26IN0427
Subject: Inorganic Chemistry · Chapter: Lanthanides and Actinides · Topic: Lanthanide And Actinide – General · Exam: GATE 2005-2021 · Marks: 2 · Difficulty: Hard
The calculated and observed magnetic moments differ considerably for an aqua complex of a Lanthanide (III) ion as a result of low lying states of high J. The ion, among the following, is
(a)$\mathrm{Ce}^{3+}$
(b)$\operatorname{Pr}^{3+}$
(c)$\mathrm{Eu}^{3+}$
(d)$\mathrm{yb}^{3+}$
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Eu³⁺ (⁷F₀ ground) has the ⁷F₁ and ⁷F₂ levels only a few hundred cm⁻¹ higher, so they are thermally populated and the observed moment (≈3.4 BM) far exceeds the g_J√J(J+1) = 0 of the ground level. Sm³⁺ shows the same effect; Ce, Pr and Yb do not.