Water-Mediated Structural Transformations of Cu II 5-Halonicotinates Coordination Networks with Distinct Mechanisms.

Currently, no unequivocal evidence is given for elucidation of "black box" during the structural transformations of dynamic crystalline materials. Here, three types of mechanisms are revealed for such transformations through X-ray diffraction and optical microscopy; namely, single-crystal to single-crystal (SC-SC), as well as "core-to-core" and "core-on-shell" processes. As confirmed by time-lapse optical microscopy, the latter two cases can be properly ascribed as partial recrystallization processes, while the former one is a continuous process with two different crystal lattices simultaneously maintained in one single crystal. Interestingly, these three distinct pathways can be exquisitely realized by changing only the halogen substituent (from -F, -Cl, to -Br) of the organic ligands in the coordination supramolecular systems.