An Open Inquiry Lab Experiment Preparing Bis(N,N-diethylethylenediamine) Nickel(II) Complexes

Starting with a double replacement reaction in alcohol between Ni(H2O)6(NO3)2 and NaX, students exploit solubility differences to produce a solution of NiX2 and a NaNO3 precipitate. They then synthesize a bis(N,N-diethylethylenediamine) Ni(II) complex with chloride, bromide, iodide, thiocyanate, acetate, nitrate, or perchlorate. Infrared spectroscopy provides very useful characterization information, especially when comparing different complexes between students. The solid complexes have different colors. Some of the complexes are high spin, and some are low spin. Students combine class data to correlate the color of the compound, magnetic susceptibility measurements, and expectations from ligand-field theory for d8 tetragonally distorted octahedral and square planar complexes. This is an open inquiry laboratory experience because students are only provided with generic instructions, students are responsible for planning what to work on next, and students modify or repeat steps as needed based on their infrared spectroscopy measurements.