Control of Structure Dimensionality and Functional Studies of Flexible Cu-II Coordination Polymers

Four Cu-II coordination polymers [Cu-2(bci)(2)(H2O)(2)]center dot 3H(2)O (1), [Cu- (tciH)(H2O)] (2), {[(Cu(tci)](2) [Cu-5(tci)(2) (OH)(2) (H2O)(8)]}center dot 22H(2)O (3), and [Cu-3 (tci)(2)(py)(4)(H2O)(2)] (4) (bciH(2): bis(2-carboxyethyl) isocyanurate; tciH(2): 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 (M) chains (1 and 2), 2D layers with 0D units (3), and 3D frameworks (4). The ID chain structure of I is formed by the bipodal ligand bciH(2) with Cu-II ions linked by the Cu-2(CO2)(4) paddlewheel secondary building units (SBUs). The structure of 2 is very similar to I, where two carboxylic acid groups of the similar tripodal ligand tciH(3) 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 Cu-5 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.