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 {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]·8H2O}n (1), [Zn3(IDC)2(bpy)(H2O)2]n (2),
and {[Zn3(IDC)2(bpy)3]·(bpy)·8H2O}n (3) (H3IDC = 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 [Cd4(μ3-HIDC)2(μ4-IDC)(μ5-IDC)]24- are linked by [Cd(bpy)2]2+ to generate
a 1D chain of {[Cd8(μ3-HIDC)4(μ4-IDC)2(μ5-IDC)2]Cd(bpy)2}n2n-, and the 1D chains are further bridged by μ2-bpy to form a 2D
brick-wall-like network of {[Cd8(μ3-HIDC)4(μ4-IDC)2(μ5-IDC)2(μ2-bpy)2]Cd(bpy)2}n2n- (≡ [Cd9(HIDC)4(IDC)4(bpy)4]n2n-). Each
“brick” contains one protonated bpy ion of H2bpy2+ to get a neutral compound of {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]·8H2O}n. The
adjacent 2D brick walls are perpendicularly packed and interlinked by μ4-IDC3- and μ5-IDC3- bridges to generate a 3D open
framework of 1. The species of μ3-HIDC2-, μ4-IDC3-, μ5-IDC3-, H2bpy2+, μ2-bpy, and monodentate bpy coexist in compound 1.
Compound 2 consists of 2D wavelike sheets of [Zn3(μ3-IDC)2(H2O)2], which are further linked through μ2-bpy to generate a 3D
structure. In 3, the 2D honeycomb-like sheets of [Zn3(IDC)2]n are bridged by μ2-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.