Just before the Thanksgiving break, Scarlett Lin Latt, an undergraduate in Jocelyn Lanorio’s lab at Illinois College made these colorful solutions of “related” cobalt compounds. She started with a light pink solution of cobalt(II) chloride hexahydrate (bottom right). Then Lin Latt added ethylenediamine to the solution to make a green cobalt complex. When heated, this complex changed the way it binds the ethylenediamine molecules—shifting from a trans isomer to a cis one—which produces the purple solution. Separately, by adding ammonia and a nitrite ligand to the original cobalt(II) chloride hexahydrate solution, Lin Latt produced the orange solution, in which the nitrite ions’ bind to cobalt through one of their oxygen atom. After letting it stand, the complex went from binding the nitrite’s oxygen to binding its nitrogen, resulting in the yellow solution.
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