Bimetallic Uranyl Organic Frameworks Supported by Transition-Metal-Ion-Based Metalloligand Motifs: Synthesis, Structure Diversity, and Luminescence Properties.

A bifunctional ligand, 2,2'-bipyridine-4,4'-dicarboxylic acid (H2bpdc), has been used in the investigation of constructing bimetallic uranyl organic frameworks (UOFs). Seven novel uranyl-transition metal bimetallic coordination polymers, [(UO2)Zn(bpdc)2] n (1), [Cd(UO2)(bpdc)2(H2O)2·2H2O] n (2), [Cu(UO2)(bpdc)(SO4)(H2O)3·2H2O] n (3), [CuCl(UO2)(bpdc)(Hbpdc)(H2O)2·H2O] n (4), [Cu(UO2)(bpdc)2(H2O)] n (5), [Co2(UO2)3(bpdc)6] n (6), and [Co3(UO2)4(bpdc)8(Hbpdc)(H2O)2] n (7), have been successfully constructed through the assembly of various transition-metal salts, uranyl ions, and H2bpdc ligands under hydrothermal conditions. UOFs 1, 5, 6, and 7 adopt three-dimensional (3D) frameworks with different architectures; UOFs 2 and 3 exhibit two-dimensional (2D) wavelike and stairlike layers, respectively, while UOF 4 is a one-dimensional (1D) chain assembly. These UOFs include a wide range of dimensionalities (1D-3D), interpenetrated frameworks, and cation-cation interaction species, suggesting that anion-dependent structure regulation based on the metalloligand [M(bpdc) m] n- motifs, the coordination modes of the metal centers and bpdc2- ligands, along with the reaction temperature, has a remarkable influence on the formation of bimetallic UOFs, which could be a representative system for the structural modulation of UOFs with various dimensionalities and structures. Furthermore, the thermal stability and luminescent properties of compounds 1, 3, and 6 are also investigated.