Coordination Sphere Flexibility Leads to Elastic Deformation in a One-Dimensional Coordination Polymer Crystal

Coordination polymers exhibiting mechanical flexibility including elastic or plastic bending are rare. Here, we report an example of a mechanically flexible one-dimensional coordination polymer that shows elastic bending. Quantitative insights on the inter and intra-chain bonding as well as structural flexibility from a combination of techniques including variable temperature single crystal X-ray diffraction (XRD), highpressure crystallography (ambient-15 GPa), synchrotron micro-XRD mapping of the bent crystal, and high-resolution synchrotron X-ray charge density analysis show that the helical coordination polymer behaves like a spring when subjected to external stimuli. Changes that occur with the variation of temperature, pressure, or bending, however, result in very different mechanistic changes. The exceptional coordination sphere flexibility rendered by the presence of Jahn-Teller distorted coordination bonds leads to the flexibility of the polymer.