Electronic spectra and nature of transitions in [NH2(C2H5)2]2CuxZn1?xCl4 (x = 0.5, 1) crystals

The absorption spectra of the NH₂(C₂H₅)₂]₂CuCl₄ crystals grown from a solution in ethyl alcohol and also of solid solutions of NH₂(C₂H₅)₂]₂Zn_0.5Cu_0.5Cl₄ in the visible spectral region have been investigated in the vicinity of thermochromic phase transitions. It is shown that the phenomenon of thermochromism in these crystalline compounds is primarily related to the replacement of the square-planar geometry of the coordination surrounding of the Cu²⁺ ion by a tetrahedral one.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 798–802, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.