Dramatic Structural Rearrangements in Porous Coordination Networks

With the use of ab initio X-ray powder diffraction, a family of isostructural crystalline porous coordination networks, [(ZnX2)3(TPT)2]n· (solvent) (X = I, Br, Cl), has been studied at elevated temperatures of 573−723 K. Upon heating, all three networks exhibited crystalline-to-amorphous-to-crystalline (CAC) phase transformations to three new networks, [(ZnI2)3(TPT)2]n, [(ZnBr2)3(TPT)2]n·(H2O) and [(ZnBr2)(μ-Br)(ZnBr)(TPT)]n, and [(ZnCl2)(μ-Cl)(ZnCl)(TPT)]n, respectively. A set of control experiments was used to obtain detailed mechanistic aspects of the CAC transformations. We demonstrate how bonds are broken and formed in these significant molecular rearrangements and how the initial arrangement plays a crucial role in the formation of the new networks after the CAC transformations. The structural information in the amorphous phase is retained and passed from a metastable to a more stable crystal, thus, reinforcing the notion that coordination networks are flexible and chemically active.