The Order–Disorder (OD) Polytypism of [Cu 2 ZnTeO 4 ] 2+ [SO 4 ·H 2 O] 2−

[Cu 2 ZnTeO 4 ] 2+ [SO 4 ·H 2 O] 2− crystallizes as a category IV order‒disorder (OD) structure with two kinds of nonpolar layers with the formal composition [Cu 2 ZnTeO 4 ] 2+ and [SO 4 ·H 2 O] 2− , respectively. Reflection symmetry that is only valid for the [Cu 2 ZnTeO 4 ] 2+ layers leads to two ways of placing the [SO 4 ·H 2 O] 2− layers. Two of the polytypes are of a maximum degree of order (MDO 1 : P 2 1 / m and MDO 2 : Pnma ). The crystal under investigation is mostly of the MDO 2 polytype. Remaining positive electron density peaks in the difference Fourier maps indicate fragments of the MDO 1 polytype.