Compound Analysis: bis(diethylammonium) tetrachlorocuprate (II)
This compound is a bright green color at room temperature and undergoes a reversible solid-state reaction to a yellow color at temperatures above 52?C-53?C.(9) At temperatures below 52?C-53?C, the four coordinate compound has a square planar geometry even though it is not a d8 compound. Because of the short hydrogen bonds between the hydrogens of the counter ion, diethylammonium, and the chlorines on the metal compound, it favors this square planar geometry. In the planar CuCl42- compound, the NH---Cl bond distance is 331 pm. When the temperature passes 53?C, the color changes to yellow because the hydrogen bonds lengthen to approximately 345 pm and the geometry changes to the much less constrained distorted tetrahedral.(10) The change in geometry changes the arrangement of the d orbitals as seen in Figure 1.