A discrete complex [Zn(tpro)₂(H₂O)₂] (1, Htpro = l-thioproline), and two structural isomers of coordination polymers, a 1D chain of [Zn(tpro)₂]n (2) and a layered structure [Zn(tpro)₂]n (3), were synthesized and characterized. The discrete complex 1 undergoes a temperature-driven structural transformation, leading to the formation of a 1D helical coordination polymer 2. Compound 3 is comprised of a 2D homochiral layer network with a (4,4) topology. These layers are mutually linked through hydrogen bonding interactions, resulting in the formation of a 3D network. When 1 is heated, it undergoes nearly complete conversion to the microcrystalline form, i.e., compound 2, which was confirmed by powder X-ray diffractions (PXRD). The carboxylate motifs could be activated after removing the coordinated water molecules by heating at temperatures of up to 150 °C, their orientations becoming distorted, after which, they attacked the activation sites of the Zn(II) centers, leading to the formation of a 1D helix. Moreover, a portion of the PXRD pattern of 1 was converted into the patterns corresponding to 2 and 3, and the ratio between 2 and 3 was precisely determined by the simulation study of in-situ synchrotron PXRD expriments. Consequently, such a 0D complex is capable of underdoing structural transformations and can be converted into 1D and/or 2D amino acid-based coordination polymers.
Keywords: ">l-thioproline; amino-acid-based coordination polymers; homochiral helices; self-assembly process; structural transformations.