Synthesis and characterizations of zinc(II) coordination polymers with tetracarboxylic acid and isomeric bis(imidazole)/bis(triazole) ligands

Four Zinc(II) coordination polymers, {[Zn2(µ4-L)(µ-mbix)2]·6H2O}n (KP1), {[Zn2(µ4-L)(µ-pbix)2]·6H2O}n (KP2), {[Zn2(µ4-L)(µ-mbtx)2]·6H2O}n (KP3) and {[Zn2(µ4-L)(µ-pbtx)2]·8H2O}n (KP4), were synthesized using the H4L (N2,N5-bis(3,5-dicarboxyphenyl)pyridine-2,5-dicarboxamide) and isomeric bis(imidazole)/bis(triazole) linkers, (mbix= 1,3-bis(imidazol-ylmethyl)benzene, pbix= 1,4-bis(imidazol-ylmethyl)benzene, mbtx= 1,3-bis(1H-1,2,4-triazol-1-ylmethyl)benzene, pbtx= 1,4-bis(1H-1,2,4-triazol-1-ylmethyl)benzene), and their structures were elucidated using methods such as elemental analysis, FT-IR spectroscopy, and single-crystal X-ray diffraction. The phase purities of the complexes were confirmed by powder X-ray diffraction (PXRD), and their thermal behaviors were investigated in the temperature range of 30–700°C using thermal analysis techniques. X-ray analysis demonstrated that the structural diversity of the CPs is influenced by the nature of the isomeric bis(imidazole) or bis(triazole) linkers. The bis(imidazole)/bis(triazole) linkers were essential in defining the dimensionality of the resulting networks. KP1 and KP3, incorporating mbix and mbtx, respectively, exhibited similar 2D structures, while KP2 and KP4, containing pbix and pbtx, formed analogous 3D frameworks. The H4L linker displayed a monodentate coordination mode to link to four zinc(II) centers, forming the backbone of the 2D networks. In KP1 and KP2, the auxiliary ligands did not significantly affect the dimensionality, whereas in KP2 and KP4, the pbix and pbtx ligands promoted the formation of 3D structures. Topological analysis showed that KP1 and KP2 adopt a kagome (kgm) topology, whereas KP2 and KP4 possess a 4,4T250 topology characterized by an 86-point symbol. Thermal analysis further indicated that, upon dehydration, KP2 and KP4 possessing 3D frameworks exhibited higher thermal stability than KP1 and KP3 possessing 2D structures.