Rare-earth transition-metal chalcogenides Ln3MGaS7 (Ln=Nd, Sm, Dy, Er; M=Co, Ni) and Ln3MGaSe7 (Ln=Nd, Sm, Gd, Dy, M=Co; Ln=Nd, Gd, Dy, M=Ni)

Ln3MGaS7 (Ln=Nd, Sm, Dy, Er; M=Co, Ni) and Ln3MGaSe7 (Ln=Nd, Sm, Gd, Dy, M=Co; Ln=Nd, Gd, Dy, M=Ni) adopt a three-dimensional framework composed of LnQ7 monocapped trigonal prisms with interesting [MQ3]4− chains and isolated GaQ4 tetrahedra lying in two sets of channels in the framework.