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This literature discussion is based on a 2022 Science paper describing a series of dilanthanide complexes with exceptional magnetic properties due to the presence of metal-metal bonding. These molecules are the first reported species to feature direct bonding between two lanthanides! The paper contains ample material for discussion of molecular symmetry and bonding, oxidation states and electron configurations, and magnetism. The handout includes a description, glossary, discussion questions, and pre-class worksheet. Additionally, the Faculty-Only files include a follow-up Exam Question with an Answer Key.
| Attachment | Size |
|---|---|
| Lanthanide Magnets Literature Discussion | 44.98 KB |
A student should be able to...
- Assign oxidation states to metal ions in organometallic complexes
- Write a ground-state electron configuration for a metal atom or ion
- Sketch and populate a simple MO diagram featuring metal-metal bonding
- Define Hund's Rule and explain its significance to the magnetic behavior of molecules
- Describe techniques used in the research paper to provide evidence of metal-metal bonding and magnetic properties
I constructed this literature discussion on the basis of a related homework question that I wrote for my upper-level Inorganic Chemistry course. The homework problem was unwieldy and did not quite get students to understand the complexities of this research or appreciate how amazing these molecules are! The next time I taught the course, I dedicated a full 75-minute class to the literature discussion according to the handout provided. This was great to give this paper the attention it deserves! The discussion was used at the end of the semester to tie multiple previous topics together and introduce ideas about magnetism. Some students were rusty on electron configurations, which had been discussed early on, so it was useful to go back through the process of constructing electron diagrams for each lanthanide ion and dilanthanide unit to show off just how large those spin multiplicities turn out to be!
The assignment assumes that students have been introduced to the concepts of Hund's Rule and electron configurations, symmetry and group theory, and assigning oxidation states in complexes. The questions about the point group and MO symmetry could be removed if this topic has not been covered. My course's coverage of magnetic behavior is rather limited, so the questions about magnetic moment, magnetic susceptibility, and coercivity could be expanded upon if this topic is more focused on.
I also incorporated a final exam question based on the literature discussion material, which is now provided in the Faculty-Only files. The exam question focused on writing electron diagrams, using Slater's Rules to determine Zeff for outer electrons, and using this to predict how the electron configuration and spin multiplicity / magnetic moment will change when the atom forms an ion. Students tended to do well on this question, as long as they remembered Hund's Rule and Slater's Rules. It is a fairly straightforward set of questions that could be used as a stand-alone exercise, even without the literature discussion.
Evaluation
I dedicated a 75-minute class day to the discussion questions, after assigning the worksheet as a pre-class exercise to be completed for participation credit.
Additionally, I included a final exam question based on the literature discussion material, which was scored out of 12 points and assessed student understanding of electron configurations, shielding, ionization, spin multiplicity, and magnetic moment.
The in-class discussion was lively and well-received, although there were some students who were disengaged due to lack of preparation (i.e. did not complete the pre-class questions adequately). Some students were rusty on electron configurations, which had been discussed early on, so it was useful to go back through the process of constructing electron diagrams for each lanthanide ion and dilanthanide unit to show off just how large those spin multiplicities turn out to be! This helped to focus the discussion on the simpler aspects of the molecular structures and spin properties which were more accessible to students, so that they didn't get too lost in the sophisticated magnetic measurements discussed later in the paper.
Additionally, students tended to score well on the related final exam question. The most common mistakes were small errors in the Slater's Rules calculation, forgetting Hund's Rule or the order of electron ionization, and small errors in the calculation of spin multiplicity or spin-only magnetic moment. Unsurprisingly, students who were unprepared/disengaged during the original discussion did not do as well on the final exam question, either.