Water-stable Ln-exclusive metal-organic framework for highly selective sensing of Fe3+ ions

The design and synthesis of high stability lanthanide complexes with ion detection has been widely attentions and certain challenges. In this work, we successfully synthesized and designed a series of 2D Ln-MOFs ([Ln2(L1)2(H2O)4]·2H2O, Ln = Tb (MOF-1), Eu (MOF-3); [Tb2(L1)2(DMF)(H2O)] (MOF-2)). Structural analysis suggests that every Ln(III) ion is surrounded by six O ions from four L1 ligands, and two oxygen atoms from water molecules of MOF-1 and MOF-3. For MOF-2, the asymmetric unit consists of two different coordination of Tb(III) ions, two L1 ligands, one coordinated dimethylformamide (DMF) and one coordinated H2O molecule. The eight-coordinated Tb1 is surrounded by five O ions/atoms and two μ2-O- ions from four L1 ligands; and one O atom from one coordinated H2O molecule, The seven-coordinated Tb2 is surrounded by four O ions/atoms and two μ2-O- ions from four L1 ligands and one O atom from one coordinated DMF molecule. The results of various metal ions sensing show that those three Ln-MOFs have high efficiency, sensitivity and specificity in the recognition of Fe3+ ions in aqueous solution. Further tests show that the minimum detection concentration of Fe3+ ions in an aqueous solution of the above three cases of Ln-MOFs is 10−6 M, and the interference of other ions in the solution can be effectively avoided.