Anion-dependent self-assembly of copper coordination polymers based on pyrazole-3,5-dicarboxylate and 1,2-di(4-pyridyl)ethylene.

By utilizing a pyrazole-3,5-dicarboxylic acid (H3pzdc) and flexible 1,2-di(4-pyridyl)ethylene (dpe) with various copper(ii) salts under the same solvothermal synthetic conditions, six novel coordination polymers, namely, {[Cu2(pzdc)(dpe)2]X}n (X = NO3- (1), ClO4- (2), BF4- (3), SCN- (4)), {[Cu(ii)4Cu(i)4(pzdc)4(dpe)6](H2O)4}2n (5), and {[Cu5(HPO4)2 (pzdc)2(dpe)3](H2O)5}n (6) were obtained. The structural diversity of compounds 1-6 depends on the starting Cu(ii) salts. Compounds 1-4 are isostructural and exhibit a 3D porous cationic pillar-layered coordination framework with lattice monoanions incorporated into the channels of the framework. When using copper(ii) sulfate as a reagent, a neutral mixed-valence Cu(i,ii) 2D + 2D → 2D parallel interpenetrated layer of 5 was obtained. In the case of a phosphate trianion, compound 6 shows a 3D coordination framework which contains μ4-HPO42- linking between Cu(ii) centers. The anion-exchange properties of 1-4 were studied. Interestingly, compounds 1-4 exhibit the irreversible chemisorption of the thiocyanate anion instead of anion exchange without the destruction of their structural framework as confirmed by PXRD, IR, UV-Vis, and AA spectroscopy. Moreover, the anion-induced structural transformation of 1-4 was observed when exchanging with an azide anion. The luminescent properties of 1-6 and exchanged products were also investigated.