Crystal structure of the thermochromic bis-(di-ethyl-ammonium) tetra-chlorido-cuprate(II) complex

In the structure of the title complex salt, (Et2NH2)2[CuCl4], the asymmetric unit consists of four unique di-ethyl-ammonium cations and three unique tetra-chlorido-cuprate anions. Two of the three anions are located with their copper atoms on independent crystallographic twofold axes, while the remaining tetra-chlorido-cuprate is located at a general position of the ortho-rhom-bic space group P21212. Two of the three Cu atoms adopt a distorted square-planar/disphenoidal geometry and the third Cu atom has a regular square-planar coordination environment. The di-ethyl-ammonium cations form an extensive hydrogen-bonded network through N-H⋯Cl inter-actions with the tetra-chlorido-cuprate anions, resulting in a two-dimensional sheet-like hydrogen-bonded network parallel to the ab direction. The complex was observed to undergo a color shift from deep green at room temperature to pale yellow at temperatures above 328 K.