Metal-organic frameworks based on a benzimidazole flexible tetracarboxylic acid: Selective luminescence sensing Fe3+, magnetic behaviors, DFT calculations, and Hirshfeld surface analyses

Four novel metal-organic frameworks constructed from benzimidazole flexible tetracarboxylic acid ligand, 1-(3,5-dicarboxylbenzyl)-1H-benzimidazole-5,6-dicarboxylic acid (H4L), have been prepared by a solvothermal method in the presence of N-donor ancillary ligands (1,10-phen = 1,10-phenanthroline monohydrate, 4,4 '-bibp = 1,4-di[pyridine-4-yl]benzene), namely, [Co-2(L)(H2O)(3)](n) (1), {[Cd-2(L)(1,10-phen)(H2O)]center dot 2H(2)O}(n) (2), {[Co-4(L)(2)(4,4 '-bibp)(2)(H2O)(7)]center dot 4H(2)O}(n) (3), and {[Ni-4(L)(2)(4,4 '-bibp)(2)(H2O)(7)]center dot 4H(2)O}(n) (4). Complexes 1 and 2 show a 3D supramolecular structure and crystallize in monoclinic space group P2(1)/c. Complexes 3 and 4 are isomorphous and crystallize in monoclinic space group P-n, and the respective metals exhibit a similar coordination environment. The H4L ligand behaved in different coordinated modes in Complexes 1-4, namely, mu(6)-eta(1):eta(1):eta(1):eta(0):eta(1):eta(1):eta(1):eta(1):eta(1) in 1, mu(6)-eta(1):eta(1):eta(1):eta(1):eta(1):eta(1):eta(2):eta(1):eta(1) in 2, there are two coordination modes (mu(5)-eta(0):eta(1):eta(1):eta(0):eta(1):eta(1):eta(1):eta(0):eta(1) and mu(5)-eta(1):eta(1):eta(1):eta(0):eta(1):eta(1):eta(1):eta(0):eta(1)) in 3 and 4. Furthermore, photoluminescence and magnetic properties have been studied. The results indicate that Complexes 3 and 4 show strong antiferromagnetic and ferromagnetic coupling through M-O-C-O-M interactions, respectively. In particular, Complex 2 can sensitively and selectively detect Fe3+ in aqueous systems, and the limit of detection (LOD) values of Fe3+ is similar to 0.19 mM.

Automated summary

Four novel metal-organic frameworks have been synthesized using a flexible tetracarboxylic acid ligand, H4L, and N-donor ancillary ligands. Different coordination modes and crystal structures were observed in the complexes. Complexes 3 and 4 display strong antiferromagnetic and ferromagnetic couplings, while Complex 2 can sensitively detect Fe3+ in aqueous systems with a limit of detection of about 0.19 mM.