Novel inorganic coordination polymers based on cadmium oxalates

Abstract

Three new cadmium oxalate coordination polymers, I-III, with extended layered structures have been synthesized in the presence of imidazole. While I was prepared by the reaction between imidazolium oxalate and Cd, II and III were synthesized from their constituents using hydrothermal methods. [Cd(C₂O₄)(C₃N₂H₄)]_∞ (I): monoclinic, space group P2₁/c (no. 14), a=8.7093(1) Å, b=9.9477(3) Å, c=8.4352 Å, β=93.796(1)°, Z=4; [Cd(C₂O₄)₂ (C₃N₂H₄)₃(H₂O)]_∞ (II): monoclinic, space group P2₁/c (no. 14), a=7.8614(2) Å, b=14.9332(3) Å, c=15.9153(4) Å β=94.587(1)°, Z=4; [Cd(C₂O₄)₂ (C₃N₂H₄) ₃(H₂O)]_∞ (III): monoclinic, space group P2₁/c (no. 14), a=11.844(2) Å, b=9.066(1) Å, c=18.583(2) Å, β=103.84(2)°, Z=4. While the structure of I is made from CdO₅N distorted octahedra linked with oxalate, II and III are built-up from CdO₆N, CdO₅N₂ distorted pentagonal bi-pyramids connected to oxalate units. The framework formulas of II and III are identical and their structures closely related. In all the cases, the networking between the Cd-O/N polyhedra and oxalates give rise to layered architectures with the amine molecules pointing in a direction perpendicular to the layers (in the inter-lamellar region). The difference in the linkages between the oxalates and the Cd atoms in I-III, produces unusual Cd-O-Cd one-dimensional chains, which have been observed for the first time.