Influence of Metal Ion on Structural Motif in Coordination Polymers of the Pseudopeptidic Ligand Terephthaloyl-bis-beta-alaninate

The combination of semiflexible terephthaloyl-bis-β-alaninate (TBbA2–) and metal ions at room temperature in aqueous solution results in the formation of five new compounds formulated as [Ca(TBbA)(H2O)3]·H2O (1), [Mn(TBbA)(H2O)2]·H2O (2), [Co(TBbA)(H2O)4]·2H2O (3), [Ni(TBbA)(H2O)4]·2H2O (4), and [Zn(TBbA)(H2O)4]·3H2O (5). Compounds 1 and 2 are two- and three-dimensional coordination polymers, respectively, possessing a 3,4L13 and sra topology. Compounds 3–5 are one-dimensional coordination polymers; 3 and 4 have a “plywood” conformation, and 5 has a zigzag conformation. The difference in the conformation of the three pseudopolymorphs 3–5 can be attributed to the different orientations of the ligand. Notably, in the reaction system of compounds 3 and 4, a second product can be obtained. Powder X-ray diffraction (XRD) studies show that these products have a structure similar to 5, indicating the existence of additional pseudopolymorphs, 3′ and 4′. Thermal and rehydration studies show that polymorphs 3′ and 4′ are transformed to 3 and 4, respectively, upon heating and rehydrating.