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 (H2 bpdc), 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)(H2 O) (2-Cu), (UO2 )2 Cu2 Cl2 (μ3 -bpdc)2 (μ2 -Hbpdc)2 (H2 O)3 ·2H2 O (2-Cu'), and (UO2 )2 Zn(μ3 -SO4 )(μ4 -bpdc)(μ3 -bpdc)(H2 O)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 )2 Zn(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.