We present a laboratory project suitable for high school though upper-division college courses that has been designed to allow students to qualitatively investigate or quantitatively generate the spectrochemical series for octahedral cobalt(III) complexes. This experiment is useful for concrete, visual demonstration of the structural and electronic properties of ligand-to-metal bonding. Water, ammonia, nitrite, oxalate, glycinate, ethylenediamine, 1,10-phenanthroline, carbonate, and cyanide are used as ligands to form the cobalt complexes. Each complex has a different color and λmax. This allows students to derive the spectrochemical series by visual inspection or UV–visible spectroscopy. At the high school level, the series can be generated from visual inspection of the colored compounds by use of the transmission color wheel. At the general chemistry level, the series can be generated from spectroscopic data using the λmax of lowest energy. In advanced courses students can calculate crystal field splitting values, Δ0, and the ordering of the spectrochemical series can be justified from a metal–ligand interaction point of view.
Riordan et al. (Thu,) studied this question.