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 (H(3)pzdc) 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, {[Cu-2(pzdc)(dpe)(2)]X}(n) (X = NO3- (1), ClO4- (2), BF4-(3), SCN- (4)), {[Cu(II)(4)Cu(I)(4)(pzdc)(4)(dpe)(6)](H2O)(4)}(2n) (5), and {[Cu-5(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 mu(4)-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.