Distinct structures of coordination polymers incorporating flexible triazole-based ligand: topological diversities, crystal structures and property studies

Abstract

Six new coordination polymers, namely {[Zn(btec)_0.5(btmb)]·2H₂O}_n (1), {[Co(btec)_0.5(btmb)(H₂O)]·3H₂O}_n (2), {[Cu(btec)_0.5(btmb)]·H₂O}_n (3), {[Cu₄(btc)₄(btmb)₄]·H₂O}_n (4), {[Co₃(bta)₂(btmb)₂]·2H₂O}_n (5), [Co(Hbta)(btmb)]_n (6) (H₄btec = 1,2,4,5-benzenetetracarboxylate, H₃btc = 1,3,5-benzenetricarboxylate, H₃bta = 1,2,4-benzenetricarboxylate and btmb = 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl), have been successfully synthesized under hydrothermal conditions. All these complexes were structurally determined by single-crystal X-ray diffraction, elemental analysis, IR, TGA and XRD. Crystal structural analysis reveals that 1 is the first example of an unusual 3D framework with (8⁶) topology containing a 2D molecular fabric structure. Complex 2 exhibits a 3D NbO network with (6⁴·8²) topology. In 3, Cu(II) ions are coordinated by anti-conformational btmb ligands to form left- and right-handed double helices, which are further bridged by the 4-connected btec⁴⁻ anions to give a 3D porous network. Complex 4 presents a rare 3D gra network structure with (6³)(6⁹·8) topology. 5 and 6 were obtained through controllable pH values of solution, 5 features a scarce binodal (3,8)-connected tfz-d framework with the trinuclear Co(II) clusters acting as nodes, whereas 6 has an extended 2D 4⁴ grid-like layer and the adjacent 2D layers are interconnected by strong hydrogen bonding interactions into a 3D supramolecular framework. The structural diversities indicate that distinct organic acid ligands, the nature of metal ions and the pH value play crucial roles in modulating the formation of the resulting coordination complexes and the connectivity of the ultimate topological nets. Moreover, magnetic susceptibility measurement of 5 indicates the presence of weak ferromagnetic interactions between the Co(II) ions bridged by carboxylate groups.