Unveiling Structure-Dynamic Processes in Crystals of 1D Cd(II) Coordination Polymers during the Elastic Flexible Events

Flexibility, an intriguing yet far from being a commonly observed property of single crystals, is highly sought after as it enables crystal application in innovative technologies. Here, we report on anisotropically elastic single crystals of two novel 1D coordination polymers (CPs) featuring bridging halides (Cl (<b>1</b>); Br (<b>2</b>)) and pyrazinamide ligands that enabled the determination of the bending mechanism and exploration of their mechanical properties. The mechanism identified distinctly differs from the mechanisms of elastically flexible molecular crystals subjected to mechanical stress and 1D plastically deformable crystals under quasi-hydrostatic pressure, the mechanisms of reconfigurable crystals uncovered thus far. By mapping the structural modification across the bent crystal <b>1</b> using microfocus synchrotron radiation, we found that both the 1D structural spine (controlling the distance between the organic ligands) and the ligands themselves adapt to the changes in external conditions. While the spine expands through the modifications of the bridging angles, causing a consequent enlargement of the metal···metal distances as going from the interior to the exterior of the bend, the ligands rotate toward linearity with the bending face. In addition, the extent of changes along the two other crystal axes is brought into a connection with the relative energies of the weakest links and crystal stiffness in those directions.