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

Hydrothermal reactions of imidazole-4,5-dicarboxylic acid (H 3 IDC), 4,4′-bipyridine (bpy), and Cd(NO 3 ) 2 ·4H 2 O under different conditions yielded four novel three-dimensional (3D) porous metal−organic frameworks (MOFs) of {[Cd 5 (IDC) 2 (HIDC)(bpy) 3 (py) 2 (H 2 O) 3 ]·2NO 3 ·2H 2 O} n ( 1 ), [Cd 5 (HIDC) 2 (IDC) 2 (py) 2 ] n ( 2 ), {[Cd 5 (IDC) 3 (bpy) 2 (H 2 O) 2 ]·NO 3 ·3.5H 2 O} n ( 3 ), and {[KCd 4 (IDC) 2.5 (bpy) 2 (H 2 O) 2 ]·1.5NO 3 ·3H 2 O} n ( 4 ). X-ray single-crystal structural analyses revealed that IDC 3− and HIDC 2− 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 μ 5 -IDC 3− in two different asymmetrical coordination modes to produce two different infinite two-dimensional (2D) layers, which are further pillared by μ 2 -bpy (in 1 ) or μ 5 -IDC 3− and μ 2 -bpy alternately (in 4 ) to form 3D porous MOFs of 1 and 4, in which the two asymmetrical coordination modes of μ 5 -IDC 3− have not been reported. In 2 and 3, the cadmium ions are interconnected by μ 5 -IDC 3− in a symmetrical coordination mode to form similar infinite 2D layers, and the 2D layers are further pillared by μ 4 -HIDC 2− (in 2 ) or μ 4 -IDC 3− and μ 2 -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.