[Cd<sup>II</sup>(bpdc)·H<sub>2</sub>O]<i><sub>n</sub></i>: A Robust, Thermally Stable Porous Framework through a Combination of a 2-D Grid and a Cadmium Dicarboxylate Cluster Chain (H<sub>2</sub>bpdc = 2,2‘-Bipyridyl-4,4‘-dicarboxylic Acid)
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The synthesis and characterization of a cadmium(II) coordination polymer, [Cd(C12H6N2O4)·H2O]n (1), is reported. A single-crystal X-ray analysis shows that compound 1 presents a noninterpenetrating three-dimensional porous host containing one-dimensional hydrophilic channels, where guest water molecules reside. The strategy in designing the 3-D framework architecture is based on a combination of two building subunits: a porous two-dimensional grid of (4,4) topology and a metal dicarboxylate cluster chain. Both subunits are assembled from the coordination of a cadmium ion with a three-connecting organic modular ligand, 2,2‘-bipyridyl-4,4‘-dicarboxylic acid (H2bpdc). The results of thermogravimetric analysis and powder X-ray diffraction study show that the framework rigidity of compound 1 remains intact upon the removal of guest molecules, and maintains the thermal stability up to 440 °C. The second-row transition-metal ions are capable of engaging higher coordination modes (e.g., hepta- and octacoordination) because of their atomic sizes and intrinsic electron configurations. Our results show that the heptacoordinated cadmium center plays an important role in the overall framework rigidity and high thermal stability of compound 1. Crystal data for 1: Cd(C12H6N2O4)·H2O, triclinic, space group P1̄, a = 6.7843(5) Å, b = 9.3299(7) Å, c = 9.4439(7) Å, α = 104.629(1)°, β = 92.324(1)°, γ = 100.416(1)°, Z = 2.
