The crystal structures of the R 3 Ag 1−δ GeSe 7 (R=La–Nd, Sm, Gd–Dy, δ=0.06–0.28) and R 3 Ag 1−δ SiSe 7 (R=La–Nd, Sm, Gd–Dy, δ=0–0.30) compounds were determined by means of X-ray single crystal diffraction (space group P6 3 ): a=1.0806(1)nm, c=0.6111(1)nm, R1=0.0280 for La 3 Ag 0.94 GeSe 7 ; a=1.0711(1)nm, c=0.60719(5)nm, R1=0.0126 for Ce 3 Ag 0.89 GeSe 7 ; a=1.0619(1)nm, c=0.6070(1)nm, R1=0.0387 for Pr 3 Ag 0.89 GeSe 7 ; a=1.0621(1)nm, c=0.60531(6)nm, R1=0.0166 for Nd 3 Ag 0.87 GeSe 7 ; a=1.0479(1)nm, c=0.60258(8)nm, R1=0.0165 for Sm 3 Ag 0.81 GeSe 7 ; a=1.0428(1)nm, c=0.60321(5)nm, R1=0.0187 for Gd 3 Ag 0.85 GeSe 7 ; a=1.0364(1)nm, c=0.60399(6)nm, R1=0.0274 for Tb 3 Ag 0.82 GeSe 7 ; a=1.0271(1)nm, c=0.6057(1)nm, R1=0.0202 for Dy 3 Ag 0.72 GeSe 7 ; a=1.0817(1)nm, c=0.60640(4)nm, R1=0.0185 for La 3 AgSiSe 7 ; a=1.0731(1)nm, c=0.6031(1)nm, R1=0.0200 for Ce 3 AgSiSe 7 ; a=1.0655(1)nm, c=0.6005(1)nm, R1=0.0221 for Pr 3 AgSiSe 7 ; a=1.0602(1)nm, c=0.5988(1)nm, R1=0.0177 for Nd 3 AgSiSe 7 ; a=1.0497(1)nm, c=0.59466(6)nm, R1=0.0378 for Sm 3 Ag 0.85 SiSe 7 ; a=1.0433(1)nm, c=0.59367(7)nm, R1=0.0206 for Gd 3 Ag 0.81 SiSe 7 ; a=1.0362(1)nm, c=0.59296(5)nm, R1=0.0161 for Tb 3 Ag 0.70 SiSe 7 ; a=1.0332(1)nm, c=0.59494(5)nm, R1=0.0115 for Dy 3 Ag 0.72 SiSe 7 . Gradual decrease of the silver amount has been observed in the series of chalcogenides. It was reported that the existence of two different positions of the silver atom implies Ag deficiency. Disordered position of the silver atom can be connected to ionic conductivity of R 3 AgTSe 7 compounds.