Three 3D Coordination Polymers Constructed by Cd(II) and Zn(II) with Imidazole-4,5-Dicarboxylate and 4,4‘-Bipyridyl Building Blocks

Three 3D coordination polymers of {(H 2 bpy)[Cd 9 (HIDC) 4 (IDC) 4 (bpy) 4 ]·8H 2 O} n ( 1 ), [Zn 3 (IDC) 2 (bpy)(H 2 O) 2 ] n ( 2 ), and {[Zn 3 (IDC) 2 (bpy) 3 ]·(bpy)·8H 2 O} n ( 3 ) (H 3 IDC = imidazole-4,5-dicarboxylic acid, bpy = 4,4‘-bipyridyl) were hydrothermally synthesized by controlling the final pH values of the solutions of ca. 6, and characterized by single-crystal X-ray diffraction. In compound 1, unprecedented “double-square” units of [Cd 4 (μ 3 -HIDC) 2 (μ 4 -IDC)(μ 5 -IDC)] 2 4- are linked by [Cd(bpy) 2 ] 2+ to generate a 1D chain of {[Cd 8 (μ 3 -HIDC) 4 (μ 4 -IDC) 2 (μ 5 -IDC) 2 ]Cd(bpy) 2 } n 2 n -, and the 1D chains are further bridged by μ 2 -bpy to form a 2D brick-wall-like network of {[Cd 8 (μ 3 -HIDC) 4 (μ 4 -IDC) 2 (μ 5 -IDC) 2 (μ 2 -bpy) 2 ]Cd(bpy) 2 } n 2 n - (≡ [Cd 9 (HIDC) 4 (IDC) 4 (bpy) 4 ] n 2 n - ). Each “brick” contains one protonated bpy ion of H 2 bpy 2+ to get a neutral compound of {(H 2 bpy)[Cd 9 (HIDC) 4 (IDC) 4 (bpy) 4 ]·8H 2 O} n . The adjacent 2D brick walls are perpendicularly packed and interlinked by μ 4 -IDC 3- and μ 5 -IDC 3- bridges to generate a 3D open framework of 1 . The species of μ 3 -HIDC 2-, μ 4 -IDC 3-, μ 5 -IDC 3-, H 2 bpy 2+, μ 2 -bpy, and monodentate bpy coexist in compound 1 . Compound 2 consists of 2D wavelike sheets of [Zn 3 (μ 3 -IDC) 2 (H 2 O) 2 ], which are further linked through μ 2 -bpy to generate a 3D structure. In 3, the 2D honeycomb-like sheets of [Zn 3 (IDC) 2 ] n are bridged by μ 2 -bpy to result in a 3D open framework with hexagonal and tetragonal channels. Compounds 1 and 2 are stable up to 320 and 400 °C, respectively, and display strong blue fluorescent emission at room temperature.