Synthesis, magnetic and fluorescence detection properties of four metal-organic frameworks based on imidazole carboxylic acid ligands

Four new metal-organic frameworks (MOFs), namely [M(HL)H2O]n (1-3) [M=Co (1), Ni (2), Cu (3)] and [Cd(HL)]n (4), were successfully structured based on imidazole carboxylic acid ligands [H3L=5-(((1H-imidazol-2-yl)methyl)amino) isophthalic acid]. X-ray single-crystal diffraction analysis showed that MOFs 1-3 possess the same two-dimensional (2D) planar structure, while MOF 4 exhibited a three-dimensional (3D) coordination network. The magnetic test results showed that MOFs 1-3 have typically antiferromagnetic behavior. The sensing experimental showed that MOF 4 could be considered as a promising bifunctional fluorescent sensor for Cu2+ and Fe3+ ions with excellent selectivity and sensitivity, and the detection limit were 4.11 μM and 4.89 μM, with Ksv values of 1.37×104 M−1 and 1.24×104 M−1, respectively. The cycling experiment illustrated the good reusability of the material. In addition, the fluorescence quenching mechanism of MOF 4 was further explored in detail.