Copper/Zinc-Directed Heterometallic Uranyl-Organic Polycatenating Frameworks: Synthesis, Characterization, and Anion-Dependent Structural Regulation.

By employing a multidentate ligand, 2,2'-bipyridine-5,5'-dicarboxylic acid (H2bpdc), with both O-donors and N-donors, five uranyl-Cu(II)/Zn(II) heterometallic coordination polymers, (UO2)Cu(μ4-bpdc)(μ3-bpdc) (1-Cu), (UO2)Zn(μ4-bpdc)(μ3-bpdc) (1'-Zn), (UO2)CuCl(μ3-bpdc)(μ2-Hbpdc)(H2O) (2-Cu), (UO2)2Cu2Cl2(μ3-bpdc)2(μ2-Hbpdc)2(H2O)3·2H2O (2-Cu'), and (UO2)2Zn(μ3-SO4)(μ4-bpdc)(μ3-bpdc)(H2O)3 (3-Zn), were prepared under hydrothermal conditions. Thermal stability and luminescent properties of 1-Cu, 1'-Zn, 2-Cu, and 3-Zn were also investigated. Isostructural compounds 1-Cu and 1'-Zn both have a three-dimensional (3D) framework built by polycatenating of two sets of paralleling two-dimensional (2D) grids with octahedral transition metal cations (Cu or Zn) as the cross-linking nodes. As far as we know, compounds 1-Cu and 1'-Zn are the first two cases that possess polycatenated networks in heterometallic uranyl-organic coordination polymers. Compound 2-Cu contains 3-fold interpenetrated 2D networks which are built by the connection of [(UO2)2(bpdc)2(Hbpdc)2]2- secondary building units and Cu(II). A one-dimensional tilted ladder-like structure in 2-Cu' is constructed by uranyl-bpdc chains connected by Cu(II) and Hbpdc-. Compound 3-Zn displays a layered-like 2D network contain an unusual [(UO2)2Zn(μ3-SO4)] unit. Interestingly, different anions could lead to the change of coordination sites of transition metal cations, resulting in structural diversity of heterometallic uranyl-organic frameworks.