Coordination chemistry often utilizes toxic metal ions such as nickel, cobalt and other transition metals. Common ligands include ethylenediamine and ammonia, both, which have severe inhalation hazards. Additionally, common oxidizing agents such as permanganate and dichromate possess carcinogenic and other health hazards. In each case, their use should be minimized. This experiment utilizes environmentally friendly 3% hydrogen peroxide to oxidize iron(II) to the environmentally benign iron(III) species followed by its coordination to less toxic ligands such as thiocyanate, salicylate, and citrate. Students combine each of the solutions together and record observations followed by similar tests of unknown solutions, which consist of unlabeled known solutions. By comparing the results from their known reactions with the results of their unknown reactions, students are able to deduce the identity of each of their unknowns. Finally, students are asked to develop a competitive complexation experiment (to determine relative ligand binding strength) where they first oxidize the iron(II) to iron(III) then add small amounts of ligands to observe representative color changes. Waste is minimized since all experiments can be performed in well plates or small test tubes.
Summary prepared March 2012 by Marc A. Klingshirn, Department of Chemistry, University of Illinois - Springfield.
Klingshirn, M. Oxidation and Coordination Chemistry Goes "Green", Chemistry, University of Illinois - Springfield, 2012