Restraints extracted from molecule-in-cluster optimizations of separate disorder components permit improved least-squares modelling of experimental crystal structures, and considering energy barriers alongside enthalpy differences further enables the distinguishing of disorder into static and dynamic.

Two dioxala-benzena­cyclo­nona­phanes differ principally by the presence of a pyrrolizine ring system in one and a pyrrolo­thia­zole ring system in the other. In the crystal of the former, mol­ecules are linked via C—HN and C—HO hydrogen bonds, forming sheets parallel to (10) while in the latter, mol­ecules are linked via C—HN, C—HO and C—HS hydrogen bonds, forming slabs parallel to (001).

A comprehensive review of hybrid lead halide perovskites based on [PbX₄]_∞ layers is presented. We use a crystallographic approach based on symmetry mode analysis to systematize key types of distortions, particularly octahedral tilting and layer shifts, in this extensive and diverse family of materials.