Crystal Field Theory (CFT) is a concept typically taught in an inorganic chemistry course that describes metal d-orbital splitting in various ligand environments.  Several instructional laboratory experiments exist that make connections between this abstract theory and macroscopically observable characteristics of transition metal complexes, such as color and magnetism.  Most of these labs involve the synthesis and characterization of complexes with a stable ligand geometry.  The newly developed project lab expands the inorganic instructor's repertoire by using complexes that change geometry with heating.  Two sets of three Ni(II) complexes, in which either the anion or ligand varies, are used to illustrate CFT.  Specifically, the first set uses [Ni(H2O)2 (N,N-diethylethylenediamine)2]Cl2, [Ni(H2O)2 (N,N-diethylethylenediamine)2]Br2, and [Ni (N,N-diethylethylenediamine)2]I2 to show the effect of the counter ion in determining both the complex's geometry and its ability to undergo either deaquation or deaquation-anation upon heating.  The second set explores the influence of ligand sterics for complexes of the general formula [Ni(H2O)2 (L)2]Br2, where L=ethylenediamine, N,N-dimethylethylenediamine, or N,N-diethylethylenediamine.  Cause and effect relationships are clear when a sample of an octahedral Ni(II) complex becomes square planar upon heating, resulting in a color change of the bulk solid.  The series of complexes studied in this lab can be used to discuss the spectrochemical series and reaction mechanisms, in addition to CFT and magnetic susceptibility.

Teaching Crystal Field Theory with thermochromatic compounds: An exploration of Ni(II) complexes with ethylenediamine derivatives

247th National Meeting (2014)

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