An Experiment in the Characterization of Coordination Compounds Ihring the pa31 ten y r a n there have heen numerousexperiments nhich :nwlve the synthesisand chnrnrteri~ntionof cwrdination compounds.' In the mam theseexperiments are performed w r r twuur thrcr lnh dnya. Ofren rttrntlons, rnuleuular weight and spectral data are used to elucidate the structure of the compound. In an attempt to produce a shorter experiment whsh employs more techniques, a new experiment was developed. The student is given an unknown coordination complex and asked to identify it, using both chemical and physical data. The student is given 500 mg of a sample that contains one of the following compounds:
Not all of these compounds were employed. Qualitative analysis is performed to determine which ions are inside and outside uf the coordination sphere of the complex. Care must be taken since some tests, such as thedetermination of NOr- with diphenylamine and sulfuric acid'destray the complex, and thus the test does not differentiate whether or not this ion is inside or outside the coordinate sphere. T o test for NHa or ethylene diamine in the coordination sphere, asodium hydroxide solution is added t o the solid, the mixture heated, and the gas tested with moist long-range pH paper. Other components inside the coordination sphere can be detected after the complex is destroyed by heating in the presence of dilute sulfuric acid. Next, a 35-mg sample of the unknown is dissolved in 40 ml water and the conductance of the resulting solutions measured. The student is expected to determine the number of ions present by comparison with a table of conductance data. The table is set up in such a manner that the student isgiven an estimate of the charge type but is not able to obtain an exact answer since the expected values are based upon an average conductance for 35 mg of sample for an average molecular weight of the possible unknowns. Finally, the spectrumof thesolution of the unknown is measured a t successive 50 nanometer intervals from 350 to550 nm. After plotting the spectrum, the student is expected to compare the spectral peaks with those of [Co(NH:MI]Clrand [Co(enhNO&I]NO:i. Other experiments have involved the matchingof spectra of known spectra with those of an unknown. Our expectation is to have the student interpret the spectral peaks in terms of the spectroscopic series. Students are asked to determine whether strong-field andlor weak-field ligands are present in the complex.Comparison with the two reference spectra gives the student a more specific indication of the ligands present. After all of the experimental work is completed, an identification of the compound is made based upon all data. One t o two 3-hr periodsshould be allowed for thecompletion of the work. A 4-hr lab would be ideal. We have one Spectronic-20 for 8-10 students and one conductance bridge for the entire section of 40-45 students. Copies of the directions given t o the students are available upon request. 'Creswell. C. J.. "Modular Laharaton Proeram SYNT-095." Willard Grant Press. Boston. 1972. Burmeister. J. L.. and Jovanovich, Inc., New York, pp. 105-113. 2Grotz, L. C., J. CHEM. EDUC., 50.63 (1973).
The College of Wooster Wooster, Ohio 44691
246 / Journal of Chemical Education
T. R. Williams L. W. Haynes
