The role of large Cl, Br, and I anions in the structures of Hg₃X₂Hal₂ (X = S, Se, Te; Hal = Cl, Br, I) and some related compounds is analyzed. The structures consist of modules — cubic subcells of halogen atoms body-centered by X anions or covalently bound groups and face-centered by Hg atoms. The leading role of the anions is confirmed by the high occupancies of the halogen atoms in characteristic families of crystallographic planes and by the predominant location of halogen atoms in the special positions.