Five novel Zn(<scp>ii</scp>)/Cd(<scp>ii</scp>) coordination polymers based on bis(pyrazinyl)-triazole and varied polycarboxylates: syntheses, topologies and photoluminescence

Five novel Zn(II)/Cd(II) coordination polymers (CPs) based on the V-shaped ligand 1H-3,5-bis(pyrazinyl)-1,2,4-triazole (Hbpt) and different polycarboxylates, {[Cd(bpt)(H2O)]&#183;ClO4&#183;H2O} (1), {[Cd4(bpt)2(suc)2.5(OH)]&#183;3H2O} (2), {[Cd4(bpt)3(1,3-bdc)2.5]&#183;4H2O} (3), {[Cd9(bpt)6(1,4-bdc)6(H2O)2]&#183;4H2O} (4) and {[Zn2(bpt)(H3bhc)(H2O)6]&#183;H2O} (5) (H2suc = succinic acid, 1,3-H2bdc = isophthalic acid, 1,4-H2bdc = terephthalic acid, H6bhc = benzene-1,2,3,4,5,6-hexacarboxylic acid), have been successfully synthesized. Their structures have been characterized using single-crystal X-ray crystallography, powder X-ray diffraction (PXRD) analyses, elemental analyses, IR spectroscopy, and thermogravimetric analyses (TGA). Complex 1 bears a two-dimensional (2D) layered (3,3) network, which is further extended into the resulting three-dimensional (3D) supramolecular architecture via π⋯π stacking interactions between the terminal pyrazine groups of bpt− ligands. In 2, Cd(II) ions and bpt− ligands construct a 2D Cd-bpt layer and two 1D zigzag chains, which are further connected by suc2− ligands to form a 2D + 1D → 3D (4,5)-connected framework. Complex 3 contains two kinds of grids, and their alternating arrangement gives a final complicated 3,4,5-connected network with a stoichiometry of (3-c)6(4-c)9(5-c)2. In 4, the bpt− ligands act as tetradentate ones to connect neighbouring Cd(II) ions into an infinite 1D Cd-bpt chain. The completely deprotonated 1,4-bdc2− ligands further link the adjacent Cd-bpt chains to generate a novel 3,4,6-connected 3D topological network with (3-c)2(4-c)14(6-c). Complex 5 displays an infinite 1D coordination chain. There are strong π⋯π stacking interactions between adjacent chains in 5 with a centroid–centroid distance of 3.860 A and 3.862 A, resulting in a 3D supramolecular structure. The results show that Hbpt can act as a versatile building block for the construction of various coordination polymers. Moreover, the fluorescence properties of 1–5 in the solid state have also been investigated.