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  Home > JCE Print > Journal of Chemical Education > Issues > 2009  > December  >
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In the Laboratory
Quantifying the Electron-Donating Strength of Phosphine Ligands
Ashley L. Morris and John T. York
Department of Chemistry, Stetson University, DeLand, FL 32720
Cover
December 2009
Vol. 86 No. 12
p. 1408

Abstract
This laboratory experiment for use in inorganic or organometallic chemistry allows students to examine the property of ligand electron-donor strength and its impact on a transition-metal center. Students synthesize a series of four cis-Mo(CO)4(PR3)2 complexes with phosphorus(III) ligands having a wide range of electron-donating strengths (PR3 = P(n-butyl)3, PPh3, P(OMe)3, and P(OPh)3). These complexes are characterized by FT-IR spectroscopy, with an A1 carbonyl stretch (νCOMo) used as a handle for quantifying the electron density of the molybdenum center. Using this data, students qualitatively rank the electron-donor strength of this series of ligands. In addition, students apply the Tolman electronic parameter (TEP), the quantitative analysis of ligand effects (QALE) model, and the molecular electrostatic potential (MESP) as quantitative measures of phosphine-donor ability. By developing linear correlations between these parameters and their experimental νCOMo data, students estimate the νCOMo values for additional cis-Mo(CO)4(PR3)2 complexes not synthesized in this laboratory. This combined qualitative and quantitative investigation provides students with practical insight into ligand-donor ability and its application in "tuning" the properties of a metal complex.
Supplement
Student handouts with synthetic details and postlab questions; Instructor notes
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Citation
Morris, Ashley L.; York, John T. J. Chem. Educ. 2009, 86, 1408.
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Keywords
Coordination Compounds; Hands-On Learning / Manipulatives; Inorganic Chemistry; IR Spectroscopy; Laboratory Instruction; Organometallics; Quantitative Analysis; Synthesis; Upper-Division Undergraduate
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History
Created:
Last Updated:
10/22/2009
11/2/2009
 Caution! 
Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
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