Coordination Assemblies of Co^II/Cu^II/Zn^II/Cd^II with 2,5-Bipyridyl-1,3,4-Oxadiazole and Dicyanamide Anion: Structural Diversification and Properties

This work presents eight coordination assemblies based on divalent metal ions (M = Co^II, Cu^II, Zn^II, and Cd^II), dicyanamide anion (N(CN)₂⁻, dca), and two isomeric bent dipyridyl coligands (L), namely, 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo) and 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo). In the resulting crystalline materials, both bpo and dca tectons generally display the bidentate bridging fashion (except in the mononuclear species 5), extending the metal centers to afford diverse one-, two-, and three-dimensional (1-D, 2-D, and 3-D) coordination networks that are not commonly observed in M−dca−L systems. Notably, the inclined polycatenated 2-D → 3-D framework and 3-D polyknotting network with the unique 6-connected (4⁴.6¹¹) topology are formed for the Cu^II and Cd^II species with dca and 4-bpo. For the polymeric Co^II and Cu^II complexes, very weak antiferromagnetic or ferromagnetic interactions are observed between the metal centers due to the μ_1,5-bridging mode of dca, and their magneto-structural correlations have been discussed in detail. The Zn^II and Cd^II complexes show solid-state fluorescent emissions at room temperature.