Hydrothermal synthesis and characterization of a series of luminescent Zn(ii) and Cd(ii) coordination polymers with the new versatile multidentate ligand 1,3-di-(1,2,4-triazol-4-yl)benzene

Abstract

Used a newly designed multidentate benzene-based bis-triazole ligand 1,3-di-(1,2,4-triazol-4-yl)benzene (L), a series of luminescent Zn(II) and Cd(II) coordination polymers, namely, {[Zn(μ₂-L)₂(H₂O)₂]·(SiF₆)·H₂O}_n (1), {[Cd(μ₂-L)₂(H₂O)₂]·(SiF₆)·2H₂O}_n (2), {[Zn(μ₂-L)Br₂]·H₂O}_n (3), {[Cd(μ₂-L)₂(NCS)₂]·2H₂O}_n (4), {[Cd(μ₂-L)(μ₄-L)](BF₄)₂}_n (5), {[Cd(μ₂-L)(μ₄-L)](ClO₄)₂}_n (6) and {[Cd₃(μ₃-L)₆](NO₃)₆}_n (7) have been isolated under hydrothermal conditions. Both 1 and 2 present 1D double chain structures, which contain two kinds of different supramolecular channels. For 3, zinc(II) ions are linked by L ligands and arranged into infinite right- or left-handed helical chains. 4 presents a 2D framework in which 1D right-handed and left-handed helical structures are interlinked via Cd(II) centers as hinges. 5 and 6 respectively contain μ₂- and μ₄-L ligands in triazole–metal complexes. These μ₄-L ligands link neighboring Cd(II) centers forming a 2D network containing infinite {Cd-(trz)₂-Cd}_n chains, which is quite different from the 2D arrangement in 4. 7 presents a novel 3D porous MOF (porous metal–organic framework) containing triangular nano-porous channels with edges of 13.622 Å, in which free NO₃⁻ anions are located. Anion exchange experiments based on 7 also indicate that NO₃⁻ anions are able to be exchanged with ClO₄⁻ anions in the solid state. Both the dihedral angles (between two triazole rings or between triazole and aromatic benzene rings) for L are flexible and ultimately tune the coordination geometries in constructing various different coordination polymers. For 1–7 the comparison between powder X-ray diffraction (PXRD) and a simulated analysis from crystal data confirmed the pure crystal phases. Solid-state luminescent properties and thermal stabilities of 1–7 also have been determined.