Syntheses and structures of two new coordination polymers generated from a 4-aminotriazole-bridged organic ligand and Co^II salts

Abstract

Organic ligands and counter-anions influence the coordination spheres of metal cations and hence the construction of coordination polymers (CPs). The specific bent geometries of five-membered heterocyclic triazole bridging organic ligands are capable of generating CPs with novel patterns not easily obtained using rigid linear ligands. A multidentate 4-aminotriazole-bridged organic ligand, namely 4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole (L) has been prepared and used to synthesize two Co coordination polymers, namely poly[[[μ-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κN:N']bis(methanol-κO)cobalt(II)] bis(perchlorate)], {[Co(CHN)(CHOH)](ClO)}, (I), and poly[[μ-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κN:N':N'']dichloridocobalt(II)], [CoCl(CHN)], (II), using CoX salts [X = ClO for (I) and Cl for (II)] under solvothermal conditions. Single-crystal X-ray structure analysis revealed that they both feature two-dimensional networks. Cobalt is located on an inversion centre in (I) and in a general position in (II). In (I), L functions as a bidentate cis-conformation ligand linking Co ions, while it functions as a tridentate trans-conformation linker binding Co ions in (II). In addition, O-H...N and N-H...O hydrogen bonds and C-H...π interactions exist in (I), while N-H...Cl and π-π interactions exist in (II), and these weak interactions play an important role in aligning the two-dimensional nets of (I) and (II) in the solid state. As the compounds were synthesized under the same conditions, the significant structural variations between (I) and (II) are believed to be determined by the different sizes and coordination abilities of the counter-anions. IR spectroscopy and diffuse reflectance UV-Vis spectra were also used to investigate the title compounds.