Control of Structure Dimensionality and Functional Studies of Flexible CuII Coordination Polymers

Publisher Website
Google Scholar
Abstract
Flexibility′s the key! Control synthesis of 1D, 2D, and 3D CuII coordination polymers of flexible ligands were performed by changing the reaction conditions. One 2D compound showed solvent-induced reversible structural transformation between crystalline and amorphous phases. The dehydrated phase of the 2D compound showed size and affinity-based selective sorption of solvents. Four CuII coordination polymers [Cu2(bci)2(H2O)2].3H2O (1), [Cu(tciH)(H2O)] (2), {[Cu(tci)]2 [Cu5(tci)2 (OH)2 (H2O)8]}.22H2O (3), and [Cu3(tci)2(py)4(H2O)2] (4) (bciH2: bis(2-carboxyethyl) isocyanurate; tciH2: tris(2-carboxyethyl) isocyanurate) were synthesized by using two flexible organic ligands at room temperature. Control synthesis of the compounds showed a variety of structural motifs, namely, one-dimensional (1D) chains (1 and 2), 2D layers with 0D units (3), and 3D frameworks (4). The 1D chain structure of 1 is formed by the bipodal ligand bciH2 with CuII ions linked by the Cu2(CO2)4 “paddlewheel” secondary building units (SBUs). The structure of 2 is very similar to 1, where two carboxylic acid groups of the similar tripodal ligand tciH3 are used to make a 1D chain structure and one carboxylic acid group of the ligand remains protonated. Use of an excess amount of base (NaOH) deprotonated all three carboxylic acid groups to form 3, which contains an anionic 2D sheet structure neutralized by the 0D cationic Cu5 units. When pyridine was used as base, it also functioned as a co-ligand to make 3D frameworks of 4. Compound 3 showed reversible structural transformations between crystalline and amorphous phases upon dehydration and rehydration. The dehydrated phase showed size and affinity based selective sorption, where MeOH molecules were adsorbed but MeCN and EtOH molecules with similar and larger sizes, respectively, were not adsorbed. The sorption profile of MeOH showed gate-opening phenomenon with a hysteresis profile, which indicates dynamic structural transformations.