In the Laboratory
A Literature-Based, One-Quarter Inorganic Chemistry Laboratory Course
W
Michael J. Baldwin Department of Chemistry, The University of Cincinnati, Cincinnati, OH 45221-0172;
[email protected] Classroom teaching, including laboratory classes in which the experiments are derived from “cookbook-style” lab manuals, often fails to convey the excitement of discovery, which is the essence of science and research (1). It is a challenge to bring the thrill of research into the curriculum of formal coursework, within the constraints of the one-quarter or one-semester timeframe by which advanced laboratory coursework is often limited. One approach to this challenge is the development of a lab course in which students are involved in a small part of an original research project. Such laboratory courses have been successfully implemented at a number of schools (1–4). However, nontrivial, original experimentation often does not lend itself to predictable time scales or results that facilitate fair evaluation of a student’s abilities. Thus, the time constraints of a one-semester, or especially a one-quarter, laboratory course may often dictate that the range of synthetic and physical techniques covered is rather limited. Finally, while it is true that good research is never “finished”, some closure is important in a student’s initial exposure to experimental chemistry. An alternative approach that addresses these concerns, albeit at the sacrifice of the students’ being directly involved in “original” research, is to reproduce a coherent series of syntheses and other experiments from judiciously chosen examples in the primary literature. Herein is described such an approach that has been used successfully at the University of Cincinnati in a one-quarter (10 week, one 3.5-hour class per week) advanced undergraduate inorganic chemistry laboratory course. This literature-based laboratory course provides a context for the experiments that draws on the atmosphere of creating new knowledge that is conveyed by good research papers. Students synthesize, characterize, and evaluate the physical and reactivity properties of complexes that are described in terms of their novelty and significance to the larger research process by the papers being used. The literature context also exposes the students to the interdisciplinary nature of modern chemical research. At the same time, this approach allows the experiments to be scheduled within the time constraints of the laboratory class period. The course employs the variety of experimental techniques for synthesis, separations, and physical methods that are suggested by the guidelines from the ACS Committee on Professional Training (5, 6). It also assures, to the extent possible, closure for the student and a predictable outcome for evaluation by the instructor. Description of Student Population The students enrolling in this course are typically chemistry majors in their junior or senior year. They have generally completed the first two quarters of a three-quarter advanced inorganic chemistry lecture series and are taking the third quarter of the lecture series concurrently with the
laboratory class. The lecture class is not a pre- or co-requisite for this laboratory class; the material in the laboratory class is independent of the lectures. The number of students taking the class has averaged about twelve per year, distributed between two sections that meet on different days of the week. This is an ideal number of students for this course, as two-person teams seem to be most effective, and the current course organization has each of three teams rotating through three experiments during a given series of class periods. Three person teams are acceptable, while more than that will likely result in some members of the teams watching rather than participating. Thus, a maximum of eighteen students distributed between two sections may be ideally accommodated by the course organization described here. Description of Course Outline and Experiments A pair of closely related papers from the Journal of the American Chemical Society were chosen as the main “text” for this course (7, 8). These papers, which describe work with manganese complexes as small-molecule models for components of the oxygen-evolving complex in photosynthesis, were chosen based on three criteria. First, they include a broad range of synthesis, physical methods, and reactivity experiments that build upon and complement each other. Second, the biological significance of the inorganic chemistry reported in the papers demonstrates to the students the interdisciplinary nature of modern chemical research and the interconnectedness of different areas of the natural sciences. Finally, the familiarity of the instructor with the work reported in the chosen papers was a significant consideration in the successful conversion of the literature reports into undergraduate laboratory projects. Certainly, many other literature reports are equally appropriate as a basis for this kind of course; the example that is described here is one that has worked well. During the first three laboratory periods, the students work individually on a series of syntheses. On the first day of class, after all of the necessary check-in and introductory procedures, they prepare the organic ligand. In the next lab period, this ligand is used to synthesize a Mn(III) complex, 1, from which a second Mn(III) complex, 2, is made. In the third lab period, the reactions of these two Mn(III) complexes with hydrogen peroxide and base are compared, and the cleaner reaction is chosen to prepare a Mn(IV) complex, 3. The next six lab periods explore the physical and reactivity properties of these complexes and others that are derived from them. For these experiments, the students work in teams of two or three people, and these teams rotate through the experiments, with three different experiments typically going on in any given lab period. The series of experiments and some of the techniques used are listed in Table 1. A more detailed syllabus and descriptions of each experiment are
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In the Laboratory
included in the Supplemental Material. W The different complexes that are synthesized, their colors, and the numbering key used in the text and Table 1 are given in Scheme I (which is not intended to provide balanced equations). At the beginning of the course, the students are given a one-to-two sentence description of the goals for each lab period. Using the Journal of American Chemical Society papers, the students write up a procedure for accomplishing the goals for the current lab period with brief descriptions of the purpose of the experiment and any techniques to be used. At the beginning of the lab period, this is exchanged for procedures described by the instructor. The students can then learn considerations that they might not have taken into account by comparing their version to the instructor’s version. After completing the experiment, each student writes a postlab report that describes what has been done, as well as discussions of related issues guided by questions from the instructor. Many of these questions solicit comparisons between the conclusions drawn from the current experiment and those done in prior lab periods. For example, a discussion of the comparison of ligand-to-metal charge transfer energies to the electrochemical reduction potential leads to consideration of the changes in molecular orbital energies with changing ligands and metal oxidation states. In addition to the prelab and postlab reports, the students submit a final report at the end of the quarter covering the experiments from the entire course as a whole, in logical rather than chronological order. This report is written in the form of a Journal of American Chemical Society article, and should take into account feedback that the students have received from the instructor through comments on the prelab and postlab reports that have been returned. This assignment is intended to make the student more comfortable reading scientific papers, having now prepared a paper in the same format. It also reinforces the connections between the vari-
ous synthetic and physical experiments done during the quarter and the bioinorganic problem being explored by the research from which the experiments were derived. Since professional scientists communicate their work both in written form and orally, the students are also required to make an oral presentation to their classmates on some topic related to the experimental work during the quarter. This presentation requires some independent literature research beyond that needed to accomplish the series of experiments. Thus, the student is speaking as the “class expert” on the topic and providing new information to the rest of the class. Student topics have included material on the bioinorganic background of the experiments, such as a description of photosystem II or other manganese-containing enzymes; discussion of one of the instruments or techniques used in the lab in more depth than is required for the assigned experiments; and discussion of papers that cite those used in the class and present work that has been published since those papers. The score assigned for the oral report takes into account the evaluation by the instructor and teaching assistants, as well as a vote by the students on the best report considering both the quality of the presentation and the amount of new information provided. Hazards Care should be taken to minimize exposure to all chemicals, including solvents, used in these experiments by use of appropriate eye protection, gloves, and use of fume hoods (especially with the chlorinated solvents and the amines). Triflic acid, HCF3SO3, is a very strong acid and extreme care should be taken in its handling. The hazards associated with use of this acid are decreased somewhat by diluting the acid to 1 M prior to dispensing to students. Care should be taken in the use of the mercury manometer to avoid spillage and exposure to mercury.
Table 1. Experiments and Techniques Employed Experiment
Techniques and Concepts Employed
Check-in and ligand synthesis
Simple organic synthesis
Synthesis of Mn(III) complexes 1 and 2
Effect of acid–base chemistry on coordination chemistry
Synthesis of Mn(IV) complex 3
Effect of acid–base chemistry on redox reaction; chemical oxidant
Protonation of 3 to 4 and 5*
Low-temperature synthesis; effect of protonation state on stability of complex, and on charge transfer transition energies
Recrystallization of 3*
Solvent of crystallization; double boiler technique
Bulk electrolysis of 1 to 6*
Electrochemical synthesis; effect of metal oxidation state on charge transfer transition energy
Electrochemical behavior of Mn complexes*
Cyclic voltammetry; rest potential; electrochemical reversibility; effect of ligand set on reduction potential
Reaction of 3 with H2O2*
Catalysis; manometry; disproportionation
Magnetic susceptibility*
Spin-state and magnetism; exchange coupling
*Done in teams of 2–3 students.
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In the Laboratory
Conclusions The course described in this paper has worked well as a means of exposing the students to both a feel for chemical research and a wide variety of synthetic and physical methods used in inorganic chemistry within the time constraints of a one-quarter laboratory course. This format has received nearly unanimous positive reviews from the student participants. The most common type of comment in the written evaluations of the course by the students indicates that they really like the idea of experiments that build on each other through the quarter. In particular, the students prefer to learn about various aspects of an area of research in some depth rather than learning a little bit each week about various unrelated topics. The second most common type of comment reflects a favorable view of using papers from the primary literature as the “text” for the class. However, a number of the students expressed some frustration about the difficulty of understanding the papers without having previously been required to use materials directly from journal articles as a text. They suggested a brief lecture at the beginning of the course providing some guidance in reading and interpreting the papers; this will be incorporated next time the course is offered. Interestingly, a number of the students indicated that while they did not like giving the oral presentation, they felt it was valuable and should be kept as part of the class. From the point of view of the instructor, the course has been a success as well. By experimenting on different aspects of one area of research, the students are able to form more connections between the different concepts and techniques. They also develop more enthusiasm for the lab work than in a more traditional “cookbook-style” lab, as voiced by the students themselves. Because the experiments reproduce published work, there are predictable endpoints (although they
are not always accomplished!) that allow the variety of techniques indicated in Table 1 to be scheduled into the quarter, and facilitate fair evaluation of the students. By the end of the quarter, many of the students were asking questions about areas not covered in the assigned experiments related to the chemistry and the metalloenzymes that the manganese complexes were intended to model. That in itself is a strong indicator of the success of the course. Acknowledgments The author acknowledges Rebecca Jones, Elizabeth Deters, and Hershel Jude, the teaching assistants during the first two years this course was offered, whose hard work and enthusiasm have been crucial to its success. The late John J. Alexander (University of Cincinnati) is also gratefully acknowledged for his support in the development of this course and for helpful suggestions in the preparation of this manuscript. W
Supplemental Material
A course syllabus, annotated handouts, and experimental instructions are available in this issue of JCE Online. Literature Cited 1. Ruttledge, T. R. J. Chem. Educ. 1998, 75, 1575–1577. 2. Kharas, G. B. J. Chem. Educ. 1997, 74, 829–831. 3. Davis, D. S.; Hargrove, R. J.; Hugdahl, J. D. J. Chem. Educ. 1999, 76, 1127–1130. 4. Vallarino, L. M.; Polo, D. L.; Esperdy, K. J. Chem. Educ. 2001, 78, 228–231. 5. “Undergraduate Professional Education in Chemistry: Guidelines and Evaluation Procedures,” American Chemical
MnIII(salpn)(H2O)2(CF3SO3)
N
N OH
MnIII(AcAc)3 + (black)
(greenish-brown) 2
HCF3SO3
HO
MnIII(salpn)(AcAc)
B.E.
MnIV(salpn)(AcAc)(PF6)
(green) 1
H2salpn (bright yellow)
(bluish-green) 6
H2O2 [MnIV(salpn)(µ-O)]2 HCF3SO3 [MnIV(salpn)]2(µ-O)(µ-OH)(CF3SO3)
(red-brown) 3
2 HCF3SO3 -80° C [MnIV(salpn)(µ-OH)]2(CF3SO3) 2
(purple)
(blue-green)
4
5
Scheme I. Generalized syntheses of the manganese compounds prepared by the students (AcAc is acetylacetonate, H2salpn is N,N´-bis(salicylidene)-1,3-diaminopropane, and B.E. is bulk electrolysis).
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In the Laboratory Society Committee on Professional Training, 1999. http:// w w w. c h e m i s t r y. o r g / p o r t a l / C h e m i s t r y ? P I D = acsdisplay.html&DOC=education%5Ccpt%5Cguidelines.html (accessed Nov 2002). 6. “Topical supplements to the Guidelines: Inorganic chemistry,” American Chemical Society Committee on Professional Training, 2000. http://www.chemistry.org/portal/Chemistry?PID=
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acsdisplay.html&DOC=education\cpt\ts_inochem.html (accessed Nov 2002). 7. Larson, E. J.; Pecoraro, V. L. J. Am. Chem. Soc. 1991, 113, 3810–3818. 8. Baldwin, M. J.; Stemmler, T. L.; Riggs-Gelasco, P. J.; Kirk, M. L.; Penner-Hahn, J. E.; Pecoraro, V. L. J. Am. Chem. Soc. 1994, 116, 11349–11356.
Journal of Chemical Education • Vol. 80 No. 3 March 2003 • JChemEd.chem.wisc.edu
