Metal–Organic Frameworks Based on a Bent Triazole Dicarboxylic Acid: Magnetic Behaviors and Selective Luminescence Sensing Properties

Abstract

Four new metal–organic frameworks (MOFs) constructed from the bent triazole dicarboxylic acid ligand 3,5-bis(4′-carboxyphenyl)-1,2,4-triazole (H2bct) have been discovered by a solvothermal method. These MOFs, [M5(μ2-H2O)2(μ3-OH)2(bct)4(H2O)8]·4H2O}n (1, M = Co; 2, M = Ni), {[Cd2(bct)2(bipy)]·5H2O}n (3) (bipy = 4,4′-bipyridine), and {[Cd(bct)(tib)]·H2O·DMF}n (4) (tib = 1,3,5-tris(1-imidazolyl)benzene), exhibit diverse coordination modes and fascinating crystal structures. The crystallographic structures, thermal stabilities, photoluminescence, and magnetic properties have been studied. 1 and 2 share the identical structural features based on planar pentanuclear clusters except for the central ions, where the one-dimensional chain structures are constructed from the pentanuclear secondary building units linked with bct2– ligands, while 3 and 4 have similar layered structures. Magnetic analyses of 1 and 2 reveal that an overall antiferromagnetic coupling within the pentanuclear Co(II) cluster nodes are observed, which can be switched to strong ferromagnetic coupling when using Ni(II) to replace the Co(II) sites. Both 3 and 4 show intense blue emission under ultraviolet excitation. Moreover, 4 can be applied as a selective sensor for quantitatively testing the concentration of acetone in water based on the luminescence quenching effect, with a quenching constant (Ksv) value of 12.89 L mol–1 in water.