Several years ago I began using a set of Ligand-of-the-Week exercises in my Inorganic course to encourage (force) students to go outside of our textbook and into the chemical reference materials and chemical literature to find examples of ligands that bind to metal ions. My motivation was to get my students to see the wonderful breadth of known metal-ligand complexes and to develop skills associated with analyzing and classifying ligands. My original paper is fairly complete and can be accessed via J. Chem. Educ. which is now available through the ACS website. Title: “Student-Directed Explorations to Learn about Ligands in an Inorganic Chemistry Course.” J. Chem. Educ. 2004, 81(8), p. 1145.
Over the years I have modified the exercise to include learning to search the Cambridge Crystallographic Data Centre (CCDC) data base. Over the course of a 10 week term, students complete somewhere between 4 and 8 Ligand-of-the-Week exercises and the questions I ask of the students become increasingly more sophisticated as they gain greater mastery of the field. I have attached two of the six ligand assignments I gave to students over the course of the 2011 Spring Term.
I also use this exercise to include visiting speakers as participants in my course. In 2010 Ken Raymond was one of four presenters (along with three only slightly terrified students) on Ligands that bind through oxygen and in 2011, Bill Jones presented a scorpionate Ligand (N-Ligand) and Cora MacBeth presented a “bio-inspired” ligand.
1. To refresh student’s skills in drawing Lewis Structures and assigning formal charge in free uncoordinated ligands.
2. To assign a charge to a ligand when bound to a metal in a given complex (not always easy) and to determine if the ligand was protonated when free and deprotonated when bound (again sometimes very easy, other times not so easy).
3. To learn to search the CCDC to find metal complexes.
4. To use the CCDC to find a name for the complex (and ligand)
5. To take a small foray into inorganic nomenclature and to learn some specific and useful symbols and practices (examples μ2, and η5, methods of assigning metal charge, inner sphere ligands versus counterions, etc)
6. To use the CCDC to give a proper literature reference.
7. As the term progresses to learn to suggest how to classify or categorize ligands (hard or soft, strong field or weak field)
8. To hone their skills in assigning point groups (via repeated practice)
Big Picture Objectives
9. To open my student’s eyes to the breadth and beauty of known metal-ligand complexes.
10. To help them take ownership of the course (giving them a near infinite slate of choices and the ability to present what interests them most)
11. To provide an informal forum for the spontaneous discussion of “odds and ends” (example: non-innocent ligands)
1. For each assignment I receive a one to two page summary of their findings where I am looking for
- a. Good Lewis structures and assignment of charge
- b. A drawing of their metal-ligand complex and correct assignment of the symmetry of that complex
- c. Good reasoning for assignment as hard or soft, strong or weak etc
- d. A “proper” reference (my students quickly learn a good reference adds about 8% to their grade, over no reference)
2. Once or twice a term, each individual student gives a 3-5 minute presentation of their ligand and metal complex where I am looking for
- a. A 3-D structure (which I help them post as a website or that they can open from the on-line version of the CCDC).
- b. Correct answers to the assigned questions.
- c. Enthusiasm!
My students develop the skills needed to find interesting metal-ligand complexes in the CCDC. They learn to observe the 3D structures and they find the rotatable images extremely helpful in assigning point groups. I also assess that this exercise helps them feel greater ownership of the course. My evidence stems from the fact that their choices become more interesting over the course of the term and they begin to have a friendly competition of finding odd and beautiful complexes. I also find that they begin to ask about when we will have our next ligand-of-the-week exercise with a sense of positive anticipation for a bit of in-class fun.