Models of Coenzyme B12. An Undergraduate Chemistry Experiment Combining Synthesis of Cob(III)aloxime Complexes and Their Characterization by 1H NMR and Cyclic Voltammetry

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 8 Issue 4 (2003) pp 248-250

Models of Coenzyme B₁₂. An Undergraduate Chemistry Experiment Combining Synthesis of Cob(III)aloxime Complexes and Their Characterization by ¹H NMR and Cyclic Voltammetry

Elizabeth A. Landis, Steven T. Scroggins, Mark H. Schofield*, Lee Y. Park*

Department of Chemistry, Williams College, Williamstown, MA 01267, mschofield@williams.edu, lpark@williams.edu
Received March 14, 2003. Accepted May 20, 2003.

Published online: 8 July 2003

Abstract. An upper level undergraduate inorganic chemistry experiment in which students synthesize a series of octahedral cobalt(III) complexes of the type Co(dmgH)₂Br(L) and Co(dmgH)₂Me(L) where L can be a variety of substituted pyridines or imidazoles is described. The electronic structure of the series of complexes can be examined using ¹H NMR spectroscopy and cyclic voltammetry. Shifts in the ¹H NMR methyl resonance can be directly correlated with the electron-donating ability of the base and, therefore, the electron density at the metal center. Similarly, cyclic voltammetric studies reveal a significant shift in the reduction potentials, consistent with changes in the electron-donating ability of the axial base, while the oxidation potentials are largely unaffected by the identity of the axial ligand.

Key Words: Laboratories and Demonstrations; inorganic; bioinorganic; synthesis; ¹H NMR; cyclic voltammetry

(*) Corresponding author. (E-mail: mschofield@williams.edu lpark@williams.edu)

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Supporting Materials:

Supporting material for this article includes information on reagents, representative NMR and cyclic voltammetric results, full NMR data for all of the methylcobaloxime complexes reported, and a handout with details provided to students in our upper-level inorganic laboratory. Materials are available in a single Zip file (138 KB) 10.1333/s00897030698a.