We modelled the disordered structure by starting from the Sr2MnO2Cu1.5S2 structure, removing the Cu + , and reducing the interlayer spacing to 7.92 Å (Fig ). A unit cell containing one Sr2MnO2S2 slab was then used to generate a one-hundredlayer supercell, with the body centring of the parent mimicked by offsetting alternate layers by ½ in x and ½ in y. Atomic positions within each slab were fixed to respect the structural parameters of the original Sr2MnO2Cu1.5S2 phase. In the refinement, each Sr2MnO2S2 slab was given individual freedom to shift in x and y relative to the next slab as well as in the z direction, allowing layers to get closer together or further apart along the c axis. The refinement gave satisfactory fits to both X-ray (Fig. ) and neutron powder data (Fig. ) and suggested a high probability of Sr2MnO2S2 slabs sliding relative to adjacent layers by 0.32(3)a +0.32(3)b, as well as those remaining at the original relative positions (Fig ). There was a strong correlation between a lack of shift between slabs in the ab planes and larger layer separations (Fig. ) consistent with remaining parent-like Sr2MnO2Cu1.5S2 layers. The occurrence of shifts of 0.32 along ab gives a new structure defined by the space group C2/m with √2a × √2b cell expansion (Fig. ). This C2/m model correlates with smaller interlayer separations and features S-S distances shortened down to 2.33 Å.