Concerning the thermochromic mechanism of copper(II) and nickel(II) complexes of N,N-diethylethylenediamine

The thermochromic mechanism of several Cu(II) and Ni(II) complexes of the type M(dieten)2X2, where dieten = N,N-diethylethylenediamine and X = inorg. anion, has not been clearly established. Pressure and thermal studies in the electronic and ir region were made. In the electronic region, the "d-d" transitions shift to the red with an increase in temp. for both Cu(II) and Ni(II) complexes. With pressure, these transitions are shifted toward the red with Cu(II) complexes and toward the blue with Ni(II) complexes. Mid-ir data are indicative of axial interaction occurring with an increase in temp. and the lack of interaction with pressure increases. Although many factors are involved in detg. these differences, and anion and steric effects are important, the dominant factor appears to be the distortion of the tetragonal metal atom environment and axial interaction between the anions and the M-N4 plane.