Effects of solvents and metal ions on the synthesis, structural diversity and magnetic properties of the 5′-nitro-[1,1′:3′,1′′-terphenyl]-3,3′′,5,5′′-tetracarboxylic acid ligand and a highly sensitive sensor for Fe3+

Abstract

Solvents and metal ions play a crucial role in the construction of metal–organic frameworks (MOFs). Four novel three-dimensional (3D) metal–organic frameworks, namely {[Co₂(nttba)(4,4′-bpy)_0.5(H₂O)₂]·0.5H₂O}_n (1), {[Co(nttba)_0.5(4,4′-bpy)_0.5(H₂O)₂]·0.5H₂O}_n (2), {[Ni₂(nttba)(4,4′-bpy)₂(H₂O)₂]·(4,4′-bpy)·11H₂O}_n (3) and {[Zn(nttba)_0.5(4,4′-bpy)_0.5(H₂O)₂]·0.5H₂O}_n (4) have been synthesized by the reaction of different metal ions (Co²⁺, Ni²⁺ and Zn²⁺), 5′-nitro-[1,1′:3′,1′′-terphenyl]-3,3′′,5,5′′-tetracarboxylic acid (H₄nttba) and 4,4′-bipyridine (4,4′-bpy) under solvothermal conditions. Among the four complexes, the synthesis methods of complexes 1 and 3 were the same except for different metal ions, while the synthesis methods of complexes 1 and 2 were the same except for different solvents and the amount of NaOH. Complexes 2 and 4 are isomorphic crystals. However, three different three-dimensional structures were obtained with different space groups and crystal systems, and the solvent void volumes of the three complexes are in the order, 3 (3D, 44.8%) > 1 (3D, 10%) > 2 (3D, 5.9%). In addition, magnetic analysis indicated that antiferromagnetic interactions exist between the neighboring metal ions in 1, 2 and 3. 4 is a highly selective and sensitive fluorescence chemosensor toward Fe³⁺ ions with good recyclability. In this work, the structure was reshaped by introducing different solvents and metal ions, and the roles and functions of the solvents and metal ions in the structure were studied, providing a feasible idea for the design and precise regulation of MOFs.