Structural properties and phase transitions in the [(EtnMe4−n)N]2CuX4 family Original Research Article

The [(EtnMe4−n)N]2CuX4 series of compounds have been synthesized, their lattice types determined by X-ray crystallography, and their phase transitions characterized by differential scanning calorimetry. The n=1 and n=2 members of the series belong to the β-K2SO4 family, while the n=3 members crystallize in a pseudo-antifluorite structure. This confirms that a small cation/anion radius ratio stabilizes the structure type of the β-K2SO4 family. The room temperature phases of the (EtMe3N)2CuX4 salts crystallize in the polar P21cn space group which corresponds to a B2u distortion at the Γ point. Two phase transitions exist below room temperature. For the (Et2Me2N)2CuX4 salts, the room temperature space group is P1121/n, which corresponds to a B3g distortion at the zone center. A single phase transition exists just above room temperature. The room temperature space group for the (Et3MeN)2CuX4 salts are I41/a, which arises through a series of four descent of symmetry steps from the parent parent antifluorite structure.