Chemical Education Today edited by Susan H. Hixson
NSF Highlights Projects Supported by the NSF Division of Undergraduate Education
National Science Foundation Arlington, VA 22230
Richard F. Jones
Sinclair Community College The Development of Innovative Laboratory Dayton, OH 45402-1460 Experiments with UV–Visible Spectrophotometer
by Peter Abeta Iyere
We received funds from the National Science Foundation to acquire a UV–visible spectrophotometer (Cary 300 BIO UV–Vis Spectrophotometer, model EL98013047) equipped with diffuse reflectance and temperature control accessories in 1997. The equipment is being used to develop innovative inorganic chemistry experiments to augment undergraduate advanced inorganic chemistry courses. The spectrophotometer has made it possible for us to design new experiments that illustrate photochromism and thermochromism in the solid state and in solution, two concepts that have been neglected in undergraduate inorganic chemistry laboratory. As a follow-up to this, I as Project Director designed an introductory inorganic chemistry course that prepares students for the advanced inorganic chemistry courses and their accompanying laboratories. We have been able to expand a one-semester inorganic chemistry course without a laboratory component at our institution to one semester of introductory inorganic chemistry and two semesters of advanced inorganic chemistry, both with laboratories, because of the financial support we received from the National Science Foundation. Problems associated with purchasing the equipment delayed implementation of the project until 1999. Nonetheless, our students have been involved in the preliminary studies, syntheses, and characterization of complexes that will be analyzed with the instrument. Descriptions of some of the experiments being developed are provided in the following paragraphs. Heat-Induced Coloration of Tetrakis(pyridine)bis(thiocyanato)nickel(II) This experiment teaches the phenomenon of thermochromism (heat-induced color change) in the solid state. Our aim is to interpret the solid-state, reversible coloration of the species obtained from the thermal decomposition of tetrakis(pyridine)bis(thiocyanato)nickel(II) using diffuse reflectance spectroscopy and available data in the literature. The thermal decomposition and bonding mode of this complex have been studied extensively (1). The color changes observed during the thermal decomposition were attributed to stepwise loss of the pyridine moiety. When we carried out a preliminary study of this compound, we found that when all of the pyridine ligands have been lost and the resulting species was allowed to cool to room temperature, it formed a mustard yellow solid that, upon warming, turned brown. The brown material returned to a mustard yellow color when it cooled (reversible thermochromism) (2). We have prepared this and other pyridine derivatives and are now
recording the diffuse reflectance spectra in the solid state at different temperatures. A considerable challenge in this experiment is accounting for the reversible color change observed. One possibility is that the color change may be due to linkage isomerism of the thiocyanate ion—a notion discussed in detail with respect to Pb(II) and Pt(II) cyanato (thiocyanato) complexes (3). This will also provide students with an opportunity to learn about the principle of diffuse reflectance spectroscopy. The Effect of Metal Ions on the Solid State Photoreactivity of β-2-Furyl Acrylic Acid This experiment is designed to test the effect of metal ions on the light-induced color change (photochromism) of β-2-furyl acrylic acid salts in solution and in the solid state. It has been shown that β-2-furyl acrylic acid undergoes photochemical reaction in solution and in the solid state (4). To determine the effect of the central metal ion on this phenomenon, students will synthesize a different metal complex of this ligand, choosing metals from different parts of the periodic table. The spectra will provide some insight into the differences in reactivity of the metal complexes and the parent acid in solution and in the solid state. For instance, the wavelength of maximum absorption of the acid monomer, (λmax =294 nm) and the nickel(II) complex (λmax =272 nm) decreases and increases respectively as the reaction proceeds in solution. By drawing from data available on the solution reactivity of this acid, students will be asked to interpret the solid-state reactivity. Furthermore, a combination of the UV– visible and IR spectra will provide useful information about the interaction between the double bond of one furan ring with the exocyclic double bond of a neighboring moiety. Metal-Induced Reduction of Bis(phosphonate)viologen Dibromide in Acidic Solution This experiment illustrates the kinetics and mechanism of redox reactions in acidic medium. It involves a one-electron reduction of functionalized viologen with aluminum, magnesium, zinc, or tin in dilute aqueous acidic solution (5). In an undergraduate experiment based on this phenomenon (6), students are required to determine the induction time in the presence of oxygen. This is similar to the clock reaction with paraquat reported earlier (7 ). Under this situation, the blue color appears only when all of the oxygen in the solution has been purged. Accordingly, it is not possible to perform the same experiment in a deaerated solution. The spectrophotometer will enable students to study the kinetics
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Chemical Education Today
NSF Highlights of the reaction spectroscopically in the presence and absence of oxygen at different temperatures. We will also be able to obtain thermal parameters for the reaction. These are some of the experiments adapted from impressive research work that will depict current research efforts in inorganic chemistry. Literature Cited 1. Nathan, L. C. J. Chem. Educ. 1974, 51, 285. 2. Iyere, P. A. The Evolution of Reversibly Thermochromic Spe-
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3. 4. 5. 6. 7.
cies during the Thermal Decomposition of Tetrakis(pyridine)bis(thio-cyanato)Ni(II)”, manuscript in preparation. Burmeister, J. L.; Basolo, F. Inorg. Chem., 1964, 3, 1587. Ghosh, U.; Misra, T. N. J. Polym. Sci. 1988, 26, 1681. Iyere, P. A. Chem. Mater. 1995, 7, 2224. Iyere, P. A. J. Chem. Educ. 1996, 73, 455. Baker, A. D.; Casadevall, A. J. Chem. Educ. 1980, 57, 515.
Peter A. Iyere teaches in the Department of Chemistry, Tennessee State University, 3500 John Merritt Blvd., Nashville, TN 37209; email:
[email protected].
Journal of Chemical Education • Vol. 77 No. 2 February 2000 • JChemEd.chem.wisc.edu
