Crystallographic Analysis of the Genesis of the Structure Symmetry of Acid Sulfates M ₃ H(SO ₄ ) ₂ (M = K, NH ₄ )

The crystallographic analysis of five compositionally similar structures shows that the R3 ¯ -symmetrical trigonal structure and two monoclinic (C2/c) structures with the ratio M:S = 3:2 that is the same for all three have identical cation sublattices and similar real configurations of atomic positions. Two structures with M:S = 9:8, with the orthorhombic symmetry (Pcan) and with its monoclinic distortion (P2 ₁ /c), have identical cation sublattices. In the first group of the structures the symmetry and pseudosymmetry are determined by the SO ₄ template symmetry, namely, axis 3. In the second group the symmetry of cation frameworks and structures in general is partially formed by three mutually perpendicular axes 4 ¯ of the SO ₄ tetrahedra.