Exploiting Dimensional Variability in Cu Paddle-Wheel Secondary Building Unit Based Mixed Valence Cu(II)/Cu(I) Frameworks from a Bispyrazole Ligand by Solvent/pH Variation

Four coordination polymers, [Cu-II(L)H2O].2DMF (1), [(CuCu2L2)-Cu-I-L-II(H2O)(pyridine)(2)].(NO3).4DMF.3H(2)O (2), [(CuCu2L2)-Cu-I-L-II(pyridine)(3)].(NO3).DMF.4H(2)O (3), and [(Cu2L)-L-II(mu-O)(DMF)].4DMF.5H(2)O (4), have been synthesized under solvothermal conditions using a single methylene-bispyrazole based carboxylic acid ligand, L, and Cu(NO3)(2). All the compounds were comprised of copper paddle wheel secondary building units (SBUs). The structural differences in 14 arise due to different compositions of the solvent system as well as pH of the medium. Compound 1 exhibited a one-dimensional (1D) double chain structure with a porous three-dimensional (3D) supramolecular network, while 2 and 3 represent mixed Cu(II)/Cu(I) based porous frameworks. MOFs 2 and 3 were obtained by systematic binding of pyridine molecules on the axial positions of Cu paddle-wheel SBU, having a rare topology, sur; bbf-3,4-Cccm and a new topology, respectively. MOF 4 is a 3D porous network containing a Cu2(mu-O)2 moiety and exhibits a 3,4,4-c net. It contains open channels with 46.9% void volume. Gas sorption studies of 4 showed the microporous nature of the framework with 66 mL g(1) of CO2 uptake at 273 K and 31 mL g(1) at 298 K with a high Qst value of 30.7 kJ mol(1) at zero loading.