Four 3D Porous Metal−Organic Frameworks with Various Layered and Pillared Motifs

Hydrothermal reactions of imidazole-4,5-dicarboxylic acid (H3IDC), 4,4′-bipyridine (bpy), and Cd(NO3)2·4H2O under different conditions yielded four novel three-dimensional (3D) porous metal−organic frameworks (MOFs) of {[Cd5(IDC)2(HIDC)(bpy)3(py)2(H2O)3]·2NO3·2H2O}n (1), [Cd5(HIDC)2(IDC)2(py)2]n (2), {[Cd5(IDC)3(bpy)2(H2O)2]·NO3·3.5H2O}n (3), and {[KCd4(IDC)2.5(bpy)2(H2O)2]·1.5NO3·3H2O}n (4). X-ray single-crystal structural analyses revealed that IDC3− and HIDC2− in 1–4 exhibit six different types of coordination modes, among them two modes are first reported in this presentation. In 1 and 4, the cadmium ions are interconnected by μ5-IDC3− in two different asymmetrical coordination modes to produce two different infinite two-dimensional (2D) layers, which are further pillared by μ2-bpy (in 1) or μ5-IDC3− and μ2-bpy alternately (in 4) to form 3D porous MOFs of 1 and 4, in which the two asymmetrical coordination modes of μ5-IDC3− have not been reported. In 2 and 3, the cadmium ions are interconnected by μ5-IDC3− in a symmetrical coordination mode to form similar infinite 2D layers, and the 2D layers are further pillared by μ4-HIDC2− (in 2) or μ4-IDC3− and μ2-bpy alternately (in 3) to form 3D porous MOFs of 2 and 3. There are two different sizes of pores in 3 and 4, while the porous sizes are uniform in 1 and 2. Compounds 1, 2, and 4 display blue fluorescent emissions in the solid state at room temperature.