In the Laboratory
Advanced Chemistry Classroom and Laboratory
edited by
Joseph J. BelBruno Dartmouth College Hanover, NH 03755
Development of a Research-Oriented Inorganic Chemistry Laboratory Course L. M. Vallarino,* D. L. Polo, and K. Esperdy Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006; *
[email protected] Introduction and Brief History of the Project The value of research as a component of undergraduate education is widely recognized, and recent efforts to introduce undergraduate students to research experience have taken various forms in the United States and other countries (1–11). During the past 20 years, the chemistry department of Virginia Commonwealth University has consistently involved undergraduate students in research through the elective research and NSF-sponsored Experience for Undergraduates (REU) programs.1,2 To make the undergraduate research experience not just a choice for a few but a standard course offering for all chemistry majors, in 1995 we undertook the restructuring of the one-semester Inorganic Chemistry Laboratory course from its traditional pattern to a research-oriented format. This endeavor has continued and the new face of this course has now become an integral feature of our curriculum. The Student Audience The Inorganic Chemistry Laboratory course is a requirement for chemistry majors who plan to receive the ACSapproved Bachelor of Science degree and is a recommended elective for other chemistry majors. The students in the course are seniors, and for most this is the last laboratory experience before graduation. Goals and Objectives The research-oriented Inorganic Chemistry Laboratory course has three general goals. The first is to challenge students to draw from all the concepts and skills learned in previous courses and put them into practice in the performance of an individual, original research project. The second is to lead students to appreciate, by direct experience, how scientific research can develop logically from a premise to a conclusion through the gathering and evaluation of experimental evidence, and how this is a continuing process because each conclusion is only a new premise. The third, and perhaps most far-reaching goal, is for the students to experience the personal satisfaction of having contributed to new work of scientific significance. Within the broad framework of these general goals, the project has several specific objectives. 1. Students should refine previously learned laboratory skills and acquire new skills, in both the synthetic and the instrumental aspects of chemistry. 2. They should gain confidence in the planning and performance of uncharted experiments.
228
3. They should learn to evaluate their results critically in a broader scientific context. 4. They should gain practice in technical writing and oral presentation. 5. They should learn to take collective responsibility for the general upkeep of a lab.
Course Organization and Requirements The official schedule of this 2-credit laboratory course is one 4-hour session per week. Occasionally a session may last up to 6 hours; extra sessions are scheduled when necessary. There are no prelab lectures and all formal instruction is done in the laboratory using a pull-down screen and overhead projector. All laboratory equipment is considered community property; students share responsibility for the cleaning of glassware, the safe collection and storage of chemical waste, and the general upkeep of the lab. On the first day of the course, the primary instructor distributes to the students a brief selection of articles from the current literature, to be studied at home. The instructor discusses the content of the articles, leading the students to recognize how these published reports raise significant questions and show the need for further investigation. On this basis, the instructor and students together formulate a research objective and outline the strategy for a group project appropriate to the available facilities and capable of reaching a meaningful endpoint within the time schedule of the course. The following week the students begin the planning and performance of their laboratory work, which continues through the semester. They work in pairs, each pair pursuing an individual aspect of the project. However, all students are in constant communication. Results are shared and discussed; problems and difficulties are also shared and the students work as a group to resolve them. No more than five pairs work in each lab session, to allow close interaction between students and instructors and to avoid a queue for instrument use. Each student keeps a research-type laboratory notebook in which all activities are recorded in the lab as they are performed. The notebooks are collected and graded periodically, the instructor’s written and verbal comments and suggestions providing feedback for improvement. At the end of the course, each student writes a final report in the format of a scientific publication. The final results of all pairs are compared and evaluated jointly by students and instructors, leading to a meaningful conclusion of the overall project. The last activity is the preparation of a poster reporting the joint results of the class. All students participate in making the poster, which they
Journal of Chemical Education • Vol. 78 No. 2 February 2001 • JChemEd.chem.wisc.edu
In the Laboratory
then present as a group to the faculty and graduate students of the chemistry department. The poster is also presented at the Undergraduate Research Meeting of the Virginia Section of the American Chemical Society, held each year at the end of April at the University of Virginia in Charlottesville. One student, representing the class, gives a talk at the Annual Meeting of the Virginia Academy of Science, which is held at the end of May. During the first five years of the project, evaluation of the students and final grading were based on the quality of the laboratory notebook (35%) and final report (20%), and on the students’ performance in the lab and contribution to group discussions and activities (45%). These criteria will be extended in the future to include homework problems that probe the students’ understanding of the scope and limitations of the instrumental methods used for the project. Short quizzes dealing with specific issues of the current work will also be given in the lab on alternate weeks. The homework problems and quizzes will provide additional evidence of the students’ progress, or lack of it; more importantly, they will serve to focus the students’ attention on aspects of the work that may otherwise be overlooked. The Research Projects The success of a research-oriented laboratory course depends largely on the choice of the research projects to be undertaken. Based on our experience of the first five years, a project should present the following features: 1. It should be sufficiently interesting and novel to stimulate and challenge the students’ imagination, yet also sufficiently simple to be fully understood by undergraduates.
O
CH3
O
C
C N H
N H
COOH
COOH
1
2 CH3
O
OCH3
O
C N H
CH3
COOH
C N H COOH
3
4 N(CH3)2
O
Cl O
C
C
N H
N H
COOH
COOH
5
6
Figure 1. Amic acids investigated: 1, N-(phenyl)phthalamic acid, HNPPA; 2, N-(4-methylphenyl)phthalamic acid, HMeNPPA; 3, N-(3,5-dimethylphenyl)phthalamic acid, HXYNPPA; 4, N-(4-methoxyphenyl)phthalamic acid, HANPPA; 5, N -(4-dimethylaminophenyl)phthalamic acid, HDiMeNPPA; 6, N-(4-chlorophenyl)phthalamic acid, HClNPPA.
2. It should have some relevance to practical applications, in order to illustrate how chemistry and chemical research are intimately related to the many aspects of human activity. 3. It should involve as many experimental aspects (synthetic and instrumental) as compatible with available facilities. 4. It should allow a meaningful end-point to be reached within the time schedule of the course. 5. It should be so structured that each student pair can pursue an individual aspect of the project without losing sight of the whole. And, the individual projects should be of comparable complexity.
A brief description of the two projects carried out by our students the past five years is given below. Both projects are in the area of coordination chemistry, which involves the interaction of organic and inorganic compounds and thus gives students an opportunity to gain experience in a wide variety of synthetic and instrumental techniques. Coordination chemistry will most likely continue to be the focus of this course in the future; however, as the range of available instruments grows, we will be able to approach new problems of wider scope and educational value.
Case History No. 1; Classes of 1997–2000 Transition Metal Complexes of N-Phenyl Phthalamate Ligands: Synthesis and Characterization The Idea behind the Project. Polyimides, a class of organic polymers that have become important as construction materials for industrial applications, often contain an appreciable percentage of non-imidated sites—that is, of amic acid sites. It has been suggested that the anions of such amic acid sites can act as ligands for metal ions, resulting in metal-containing polymers that would combine the original properties of the host polymer with the specific properties of the guest metal ions (12). Graduate-level research in the VCU Chemistry Department had addressed some aspects of this problem (13–15), but questions still remained. Do the anionic amic acid sites of polyimides coordinate to metal ions, and if so, what is the mode of coordination? If coordination does not occur, which other reaction, if any, will take place? The Project. The coordinating ability of the amic acid sites of polyimides was investigated through the study of metal complexes of representative monomeric models. The amic acids shown in Figure 1 were chosen because their backbone structure and potential donor sites closely resemble those of technically important polyimides. Furthermore, these amic acids offer the opportunity to investigate how the metalbinding properties are influenced by the nature and position(s) of the substituent(s) in the aromatic moieties. The metal ions of choice were cobalt(II), nickel(II), copper(II) and zinc(II), which have the same ionic charge and nearly identical sizes but different spectral and magnetic properties, which can provide structural information. The students synthesized the amic acids by condensation of phthalic anhydride with aniline or a substituted aniline. The metal complexes were obtained by anion-displacement reactions from the metal acetates. All products were characterized by an appropriate combination of techniques: (i) preliminary purity check of samples by optical microscopy, (ii) elemental
JChemEd.chem.wisc.edu • Vol. 78 No. 2 February 2001 • Journal of Chemical Education
229
In the Laboratory
microanalyses (C, H, N%, by Atlantic MicroLab, Atlanta, GA) and thermogravimetric analyses to confirm the solvent content, (iii) UV, vis, and near-IR absorption spectra both in solution and in the solid state, and (iv) proton NMR spectra in solution (for the organic compounds and the diamagnetic Zn(II) complexes). Summary Results. All four amic acids shown in Figure 1 reacted with the acetates of Co(II), Ni(II), and Cu(II) to give complexes of the type {ML2(solvent)n}, where M is a metal ion, L is the amic acid anion, and the solvent is water, methanol, or a combination of both. With Zn(II) acetate, the amic acids HANPPA or HXYNPPA reacted similarly, but HNPPA and HMENPPA did not form Zn(II) complexes. Instead, the imides of the two acids were produced in good yields. The complexes of Co(II) and Ni(II), and those of Zn(II) when obtained, had very similar general properties. On the basis of the d–d electronic absorption spectra of the solid Co(II) and Ni(II) complexes, and of the proton NMR spectrum of the Zn(II) analog, these complexes were assigned a monomeric structure in which the amic acid anions act as tridentate chelating ligands via the amide and bidentate carboxylate groups. The Cu(II) complexes, which were insoluble in most solvents and had d–d-electronic spectra identical to the spectrum of the dimeric, carboxylate-bridged Cu(II) acetate monohydrate, were tentatively assigned a similar structure. Comments and Prospects for Future Work. Many of the results summarized above agree with what could have been anticipated from general considerations. What was not anticipated is the facile imidation of HNPPA and HMENPPA in the presence of Zn(II) acetate. The formation of these imides usually requires drastic conditions (e.g. heating in the solid state to a high temperature), yet in the presence of Zn(II) acetate it occurs rapidly in methanol solution at room temperature. The reasons for this behavior, which is both surprising and potentially important, is still under investigation by students in the class of 2000; if necessary, the study will be continued in future classes using other amic acids with different electrondonating or electron-withdrawing substituents in the aromatic moieties.
Case History No. 2; Classes of 1995 and 1996 Synthesis of Metal Complexes of Macrocylic Ligands Using Different Metal Salts Templates The Idea behind the Project. Complexes containing a lanthanide(III) ion bound into the 6-nitrogen-donor macrocyclic cavity illustrated in Figure 2 have potential biomedical applications (16, 17 ). For example, the luminescent complexes of europium(III) can serve as markers in cytology and immunology, provided they contain functional groups for linking to biosubstrates. The complexes of gadolinium(III) would be useful as contrast agents for in vivo magnetic resonance imaging if their tolerance were enhanced by appropriate substituents in the macrocyclic ligand. Functionalization of these macrocycles is therefore an area of current interest and a few examples of symmetrically disubstituted as well as monosubstituted complexes have been reported (18). Disubstituted macrocycles of this type can exist as two constitutional isomers that differ in the relative points of attachment of the substituents (5,14- or 5,15-positions, according to the numbering scheme of Fig. 2). Also, since the
230
3+
17
18
1
2
N
N
15
N
16
4
M3+
14 13
7
N 12
3
5 6
(X−)3
N N 11
10
9
8
Figure 2. Schematic formula of a lanthanide(III) complex of the 6-nitrogen-donor macrocyclic ligand C22H26N6, with numbering scheme of the cavity atoms.
carbon atom to which each substituent is attached is a stereocenter, each constitutional isomer can exist as stereoisomers (19). A first question was then formulated: Can the use of different metal salt templates provide some degree of isomer selectivity? Before this question could be addressed efficiently, however, a second question had to be answered: Which metal salts are effective templates for the synthesis of this type of macrocyclic complex? The Project. The students of the 1995 class addressed the second of the two questions, taking the unsubstituted macrocyclic complexes as models and screening various metal ion– anions combinations as templates. The anions of choice were acetate, trifluoromethylsulfonate, and chloride. Metal ions were chosen among those with fairly large ionic radii, as they would be expected to fit better into a large macrocyclic cavity. Only diamagnetic metal ions were used (La(III), Lu(III), Y(III), Ca(II), Sr(II), Ba(II), Pb(II)), to permit characterization of the products by 1H NMR spectra. The results showed that the ionic radius of the metal is indeed a determining factor in template effectiveness, useful values ranging from 140– 145 pm for Sr(II) and Pb(II) to 112–118 pm for Lu(III) and Ca(II). However, no rationalization could be offered for the contrasting effects of salts containing the same metal ion but different anions. Using the above results as background, students of the 1996 class addressed the first question and investigated the synthesis of the dihydroxymethyl-substituted macrocycles of La(III) trifluoromethylsulfonate and the dimethyl-substituted macrocycles of Sr(II) trifluoromethylsulfonate. The work involved the multistep synthesis of the diamine precursors, both S and R,S forms, and the synthesis and characterization the complexes. The structures of the isomeric complexes were established from proton, carbon and two-dimensional NMR spectra. Comments and Prospects for Future Work. The results of the class of 1995 provided a useful empirical guideline for the selection of effective templates in the synthesis of macrocycles of this type. The class of 1996 identified a promising example of isomer selectivity in template synthesis, but the project was discontinued because any further study of these systems would have required the availability of a high-field NMR instrument for undergraduate use. Such an instrument has recently been acquired and the project will be reopened for investigation in future years.
Journal of Chemical Education • Vol. 78 No. 2 February 2001 • JChemEd.chem.wisc.edu
In the Laboratory
Evaluation of Project Effectiveness
Notes
The evaluation of the teaching effectiveness of a laboratory course that utilizes chemical research as an instructional tool presents unusual features. The level of attainment of the specific objectives is easily assessed. The students’ progress in experimental proficiency is directly observable by the instructors who are with the students in the lab throughout the course. The lab notebooks provide the opportunity to judge how well the students have learned to keep a complete and effective record of their experimental work. The final research reports show how well the students understand the scope and significance of their results in the perspective of the original goals, and how well they have learned to present the results in a technically valid format. In all these aspects, the course has proved to be very successful. Both the organic and inorganic syntheses involved were relatively straightforward, yet they required repeated adjustment of experimental conditions (choice of solvent, temperature, and procedure); as the course progressed, we saw the students develop critical judgment in the planning and performance of their work. We saw them gradually gain confidence and skill in the use of instruments. We saw the content and organization of their notebooks greatly improve throughout the course as a result of the instructor’s feedback. We saw the students develop some level of technical writing ability through repeated rewriting of the final reports. The achievement of the general learning goals is more difficult to assess. For this, we have depended to a large extent on our close interaction with the students throughout the course and on the anonymous students’ comments in the endof-the-course evaluation forms. The comments have been unanimously very positive. Some quotes:
1. Research Experience for Undergraduates at Virginia Commonwealth University; J. Topich, NSF-sponsored REU project, 1993–96. 2. Practices and Perspectives; S. M. Ruder and S. P. Watton, NSF-sponsored REU project, 1999–2001.
I am confident that I can run my own experiments now without supervision. It was a new experience to be part of a research team. It was interesting to compare my work with that of other groups and monitor differences between our compounds. I enjoyed this lab very much and I have learned a lot. It was a good and mature lab group. Course was interesting. Everyone was treated like an adult. I learned a lot. Learning was fun and interesting.
These are mature students, ready to enter graduate or professional school or to move on to careers in industry; their evaluation of this project is a significant index of its success.
Literature Cited 1. Kharas, V. J. Chem. Educ. 1997, 74, 829–831. 2. Dunn, J. G.; Phillips, D. N.; van Bronswijk, W. J. Chem. Educ. 1997, 74, 1186–1187. 3. Dunn, J. G.; Phillips, D. N. J. Chem. Educ. 1998, 7, 866–869. 4. Victoriano, L. I.; Carbacho, H. V.; Parragues, L. J. Chem. Educ. 1998, 75, 1295–1297. 5. Whipple-VanPatter, G. J. Chem. Educ. 1998, 75, 1210. 6. Craig, N. C. J. Chem. Educ. 1999, 76, 595–597. 7. Dibble, B. G. J. Chem. Educ. 1999, 76, 886–887. 8. Slezak, J. J. Chem. Educ. 1999, 76, 1054–1055. 9. Davis, D. S.; Hargrove, R. J.; Hugdahl, J. D. J. Chem. Educ. 1999, 76, 1127–1130. 10. Mills, N.; Malachowski, M. J. Chem. Educ. 1999, 76, 1320–1321. 11. Ruttledge, T. H. J. Chem. Educ. 1998, 75, 1575–1577. 12. Shillady, D. D.; Vallarino, L. M.; Gootee, W. A. Proc. ACS Div. Polym. Mater. 1984, 51, 72–75. 13. Stoakley, D. M.; Shillady, D. D.; Vallarino, L. M.; Gootee, W. A; Smailes, D. L. In Recent Advances in Polyimide Science and Technology; Weber, W. D.; Gupta, M. R., Eds.; Proceedings of the 2nd International Conference on Polyimides: Chemistry, Characterization, and Applications; Ellenville, NY, 1985; MidHudson Section, Society of Plastics Engineers: Poughkeepsie, NY, 1987; pp 417–427. 14. Gootee, W. A. Study of Metal Ions in Polymers: Model Compounds for the Inclusion of Lanthanides in Polyimides and Bifunctional Lanthanide(III) Macrocyclic Complexes; Ph.D. Dissertation, Virginia Commonwealth University, Richmond, VA, 1989. 15. Esperdy, K.; Shillady, D. D. In Proceedings of International Symposium on Clusters and Nanostructure Interfaces; Jena, P.; Khanna, S. N.; Rao, B. K., Eds.; World Scientific: River Edge, NJ, 2000; pp 191–196. 16. Vallarino, L. M. J. Less Common Metals 1989, 149, 121–132. 17. Adeyiga, A. M.; Harlow, P. M.; Vallarino, L. M.; Leif., R. C. Proc. SPIE—Int. Soc. Opt. Eng. 1996, 2676, 212–217. 18. Vallarino, L. M. J. Alloys Compd. 1997, 249, 69–75. 19. Benetollo, F.; Bombieri, G.; Gootee, W. A.; Fonda, K. K.; Samaria, K. M.; Vallarino, L. M. Polyhedron 1998, 17, 3633–3642.
JChemEd.chem.wisc.edu • Vol. 78 No. 2 February 2001 • Journal of Chemical Education
231
