Strong strain shuttering ferroelastic crystals that self-heal after releasing the strain have been revealed for a new metal–organic framework [Cd(BDC)(AZPY)]_n (BDC = terephthalic acid; AZPY = 4,4′-azobispyridine), with the Cd(II) cation hepta-coordinated. It has been obtained in the form of single crystals without and with guests, acetonitrile or DMF (dimethylformamide). This pleochroic porous complex, hereafter referred to as AMU3, is built of two interwoven frameworks with the planar AZPY linkers (C_2h symmetric) orientationally disordered on the D_2h sites. The disorder of AZPY linkers persists down to 100 K at least, but it is eliminated by high pressure. The onset of AZPY ordering in the 0.2–0.9 GPa range depends both on the guest and on the hydrostatic fluid. The mechanism of AMU3 ferroelasticity involves the AZPY disordering in prototypic orthorhombic phase α of space-group Cmce. The AZPY ordering reduces the symmetry of phase β to monoclinic subgroup P2₁/n. The shear strain in the bulk of ferroelastic orientational-state domains is accommodated by the tilts and conformational changes of the ordered AZPY linkers, while along the boundaries between domains the Cd–N bonds break. On releasing the pressure the Cd–N bonds are restored and the signs of the cracks disappear.

Porous 1,2-bis[2-methyl-5-(pyridyl)-3thienyl] cyclopentene cocrystal with 1,4-diiodotetrafluorobenzene exhibits large negative linear compression correlated with the shape of pores.

Comprehensive investigations revealed a pressure–temperature phase diagram for 2D hybrid perovskite MHy₂PbI₄, demonstrating its high structural elasticity and ability to generate polar phases mimicking its ferroelectric analogue MHy₂PbBr₄.

The common property of all materials is their elasticity, directly related to the chemical components and interactions in their structure. However, the progress in constructing better devices is irreversibly tied to the understanding and designing of static or dynamic structural responses of strained materials. Such structural-property relationships have been explained for polymeric frameworks involving flexible 1,6-hexanediamine (HDA) linkers, with discrete HDA conformers. In the structure of ambient-pressure polymer Cd(HDA)₂(NO₃)₂ the HDA linkers are conformationally disordered. This tetragonal phase α is stable down to 190 K, when the HDA linkers order in different conformations, which triggers a ferroelastic transition to the triclinic phase δ; the flash-cooling of phase α overcools it to 100 K. High pressure induces a ferroelastic transition to triclinic phase β at 1.10 GPa, followed by an isostructural transition to phase γ at 2.00 GPa. All four phases α–δ differ in the configurations of HDA conformers and Cd-coordination involving nitrate linkers. The unusual convex-shaped monotonic compression of Cd(HDA)₂(NO₃)₂ phases α, β and γ has been explained by the mechanism of buckling-sticks: the increasing strain and mounting energy accumulated in the buckling HDA linkers is released by their conversions to shorter conformers. An analogous conformational transition takes place in Cd₂(HDA)₃(NO₃)₄ at 1.50 GPa. In another polymer Cu(HDA)₂(MeCN)₂·2BF₄ the conformational changes induce its very high compressibility and partial amorphization above 1.20 GPa, caused by the non-coordinated conversions of the HDA conformers.