Crystal Structures of KCuCl3 and NH4CuCl3

The crystal structures of the isomorphous garnet-red copper salts, KCuCl3 and NH4CuCl3, have been determined. Each compound contains discrete, planar, Cu2Cl6= dimers. These dimers are stacked above each other along the crystallographic a axis. The cation exhibits a ninefold coordination. KCuCl3 is antiferromagnetic below 30°K. Both KCuCl3 and NH4CuCl3 are pleochroic with maximum visible absorption when the electric vector is parallel with the Cu–Cu vector of the dimer.