Noncentrosymmetric rare-earth copper gallium chalcogenides RE3CuGaCh7 (RE=La-Nd; Ch=S, Se): An unexpected combination

The chalcogenides RE3CuGaCh7 contain monovalent Cu in trigonal planes and trivalent Ga in tetrahedra; they are electron-deficient representatives of La3CuSiS7-type compounds, which normally satisfy charge balance.