A soft porous material [Zn(L)₂(OH)₂]_n·Guest (where L is 4-(1H-naphtho[2,3-d]imidazol-1-yl)benzoate, and Guest is water or methanol) exhibits the strongest ever observed negative area compressibility (NAC), an extremely rare property, as at hydrostatic pressure most materials shrink in all directions and few expand in one direction. This is the first NAC reported in metal–organic frameworks (MOFs), and its magnitude, clearly visible and by far the highest of all known materials, can be reversibly tuned by exchanging guests adsorbed from hydrostatic fluids. This counterintuitive strong NAC of [Zn(L)₂(OH)₂]_n·Guest arises from the interplay of flexible [−Zn–O(H)−]_n helices with layers of [−Zn–L−]₄ quadrangular puckered rings comprising large channel voids. The compression of helices and flattening of puckered rings combine to give a giant piezo-mechanical response, applicable in ultrasensitive sensors and actuators. The extrinsic NAC response to different hydrostatic fluids is due to varied host–guest interactions affecting the mechanical strain within the range permitted by exceptionally high flexibility of the framework.

The crystals of the small rigid molecule 4-bromobenzonitrile exhibit highly flexible plastic bending behaviour that occurs on two perpendicular faces of the crystal, a rare situation, leading to the formation of helical/twisted and curled crystals.

A nitromethane solvate of 18-crown-6 was investigated by means of variable-temperature single-crystal X-ray diffraction in response to a report of abnormal unit cell contraction. Exceptionally large positive thermal expansion in two axial directions and negative thermal expansion along the third was confirmed. The underlying mechanism relies exclusively on weak electrostatic interactions to yield a linear thermal expansion coefficient of −129 × 10⁻⁶ K⁻¹, the largest negative value yet observed for an organic inclusion compound.