Temperature‐Reliant Dynamic Properties and Elasto‐Plastic to Plastic Crystal (Rotator) Phase Transition in a Metal Oxyacid Salt

Although, dynamic crystals are attractive for use in many technologies, molecular level mechanisms of various solid‐state dynamic processes and their interdependence, remain poorly understood. Here, we report a rare example of a dynamic crystal (1), involving a heavy transition metal, rhenium, with an initial two‐face elasticity (within ≈1 % strain), followed by elasto‐plastic deformation, at room temperature. Further, these crystals transform to a rotator (plastic) crystal phase at ≈105 °C, displaying exceptional malleability. Qualitative and quantitative mechanical tests, X‐ray diffraction, μ‐Raman and polarized light microscopy experiments reveal that the elasto‐plastic deformation involves both partial molecular rotations and slip, while malleability in the rotator phase is facilitated by reorientational motions and increased symmetry (slip planes). Our work, connecting the plastically bendable (1D or 2D) crystals with the rotator phases (3D), is important for designing multi‐functional dynamic crystals. Hierarchical mechanical responses, from elastic and elasto‐plastic bending to exceptional malleability, have been realized at different stress and temperature conditions in crystals of a rhenium oxyacid salt. The extent of the molecular rotations/translations in the mechanism is governed by the crystal structure.