The crystal structures of the Ag 2 . 6 6 Hg 2 Sn 1 . 3 4 Se 6 and Hg 2 SnSe 4 compounds were investigated using X-ray powder diffraction. The Ag 2 . 6 6 Hg 2 Sn 1 . 3 4 Se 6 compound crystallizes in an orthorhombic unit cell (space group Imm2, a=1.2795(2), b=0.42631(6), c=0.58207(4) nm). The Hg 2 SnSe 4 compound crystallizes in the thiogallate structure (defect chalcopyrite) (space group I 4, a=0.57770(2) and c=1.15570(7) nm). Atomic parameters were refined in the isotropic approximation (R I =0.0770 and R I =0.0582 for Ag 2 . 6 6 Hg 2 Sn 1 . 3 4 Se 6 and Hg 2 SnSe 4 , respectively).