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JCE Featured Molecules
William F. Coleman Wellesley College Wellesley, MA 02481
Molecular Models of Metal Complexes of Dithiocarbamates JCE Featured Molecules for October 2009 Our focus this month is on the dithiocarbamate (DTC) complexes whose synthesis is described in the paper by Malin Backlund Walker, Kimberly Edwards, and Patrick J. Farmer (1). Molecules added to the collection include disulfiram, the diethyldithiocarbamate anion (deDTC), and copper and zinc complexes of diethyldithiocarbamate (Figure 1). Dithiocarbamate complexes are found for both transition metals and main group elements, and have broad applications in medicine and other fields, as mentioned in ref 1. One might envision introducing the primary literature to a group of students, in either majors or nonmajors courses, with assignments that involve finding how such complexes are currently being used, and the nature of ongoing research involving these species. Additionally, Volume 53 of Progress in Inorganic Chemistry is devoted entirely to dithiocarbamate complexes across the periodic table (2). Dithiocarbamate complexes are also interesting from a structural viewpoint. They exhibit a wide range of coordination geometries and modes of bonding. Diethyldithiocarbamate is found as a unidentate ligand, a bridging ligand, and as a bidentate in both symmetrical and unsymmetrical environments (3). These complexes can serve as the basis for a number of exercises in computational chemistry. Included in the collection are the copper(II) and zinc(II) complexes synthesized in ref 1. The structures that are given arise from DFT (B3LYP/631-G(d)) calculations on gas phase molecules. The copper complex has a slightly distorted square planar arrangement about the copper, and the zinc complex, as expected, shows a distorted tetrahedral coordination structure. Students could be asked to predict, and then calculate, structures with different metals and/or different oxidation states, to assess the effect of these on the overall structure. They might find that the calculations are more tractable using model compounds, and included here is a copper complex with dithiocarbonate that might serve as a starting point for calculation. Many other questions could be
disulfiram
addressed computationally, and by comparison with crystal structures. The Cambridge Structural Database includes many molecules that can be used both for comparison to calculated results, and for examining the range of geometries supported by DTC ligands (4). Students could evaluate the energy differences between “pure” square planar (for copper) or tetrahedral (for zinc) geometries, and the geometries found by calculation. Our DFT calculations on the model copper complex show no imaginary frequencies for the minimum energy structure, while an idealized structure with square planar geometry exhibits two such vibrations, both leading to out-of-plane distortion of the copper–sulfur linkages. Literature Cited 1. Walker, M. B.; Edwards, K.; Farmer, P. J. J. Chem. Educ. 2009, 86, 1224–1226 and references therein. 2. Progress in Inorganic Chemistry, Volume 53; Karlin, K. D., Ed.; Wiley: New York, 2005. 3. Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th ed.; Wiley and Sons: New York, 1988. 4. Cambridge Structural Database (CSD). http://www.ccdc.cam. ac.uk/products/csd/ (accessed Aug 2009).
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/Oct/abs1.html Full text (HTML and PDF) with images in color Links to cited URLs and JCE article Supplement Find Molecular Models of Metal Complexes of Dithiocarbamates in the JCE Digital Library at http://www.JCE.DivCHED.org/ JCEWWW/Features/MonthlyMolecules/2009/Oct/.
The molecules added to the collection this month include: disulfiram
diethyldithiocarbamate anion
copper and zinc complexes of diethyldithiocarbamate
copper complex of diethyldithiocarbamate
Figure 1. Disulfiram and a copper complex of diethyldithiocarbamate. Disulfiram is an FDA-approved drug used in alcohol-aversion therapy. It has been shown to have a high and selective toxicity towards melanoma cancer in vitro; this toxicity is dependent on the presence of metal ions and suggests that the active agent is likely a Cu complex, bis(diethyldithiocarbamate)Cu(II) or Cu(deDTC)2, which is formed in situ (1).
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Journal of Chemical Education • Vol. 86 No. 10 October 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
