Continuous and discontinuous thermochromism of copper(II) and nickel(II) complexes with N,N-diethylethylenediamine

The ir spectra of trans-[ML2]X2 (M = Cu, Ni; L = Et2NCH2CH2NH2; X = BF4-, ClO4-, NO3-) are reversibly temp. sensitive. An increase of temp. causes a red shift in the visible absorption band of the Cu complexes, and the d-d absorption bands of the thermochromic Ni complexes also shift to lower frequencies with increasing temp. From differential scanning calorimetry (DSC) in the temp. range between -100° and the melting decompn. temp. (∼200°), these compds. which show a sharp spectral transformation also show an endothermic transition. The transition temp. measured by DSC is identical with that detd. spectroscopically. Thermogravimetric anal. shows that there is no wt. change on heating.