Four calcium(II) coordination polymers based on 2,5-dibromoterephthalic acid and different N-donor organic species: syntheses, structures, topologies, and luminescence properties

By using different N-donor organic species as additional auxiliary ligands with structure-directing roles, four three-dimensional (3D) calcium-based coordination complexes, [Ca(dbt)(H2O)](n) 1, [Ca(H-dbt)(2)(5,5'-dmbpy) (2)](n) 2, (4,4'-bpy)(0.5)[Ca(dbt)(H2O)(2)](n) 3, and (H-2-dib)[Ca-3(dbt)(4)(H2O)(4)center dot 2H(2)O](n) 4 (H-2-dbt = 2,5-dibromoterephthalic acid, 2,2'-bpy = 2,2'-bipyridine, 5,5'-dmbpy = 5,5'-dimethyl-2,2'-bipyridine, 4,4'-bpy = 4,4'-bipyridine, dib = 1,4-di(1H-imidazol-1-yl) benzene), have been successfully synthesized under similar solvothermal conditions and structurally characterized. The organic amine molecules play different roles in the formation of four different metal-organic skeletons with diverse structural topologies, in which complexes 1-3 are neutral, and 4 comprises a negatively charged framework with diprotonated dib as the counterion. Complex 1 features a 3D (6, 6)-connected framework structure composed of edge-sharing 1D Ca-O-Ca inorganic chains and dbt ligands. The 2,2'-bpy molecule plays an important role in the synthesis of 1 as the structure-directing agent (SDA). Complex 2 shows a 3D 2-fold interpenetrated diamondoid framework (dia, 6(6)) formed by single metal nodes via linear H-dbt anions and bidentate chelating 5,5'dmbpy ligands, while complex 3 exhibits a 3D noninterpenetrated pcu network with {4(12). 6(3)} topology constructed from binuclear [Ca-2(CO2) (4)] secondary building units and two types of dbt ligands, in which 4,4'-bpy molecules are ordered within the 3D neutral calcium-based framework as template and space filling agents. Complex 4 is a unique (4,4,4,4,5)-connected 5-nodal topology net, in which the diprotonated dib molecules provide space filling to balance the negatively charged framework. In addition, the thermal stability and the fluorescence properties of complexes 1-4 have been investigated.