Two series of Ln-MOFs by solvent induced self-assembly demonstrating the rapid selective sensing of Mg2+ and Fe3+ cations

Abstract

Two series of lanthanide-based metal–organic frameworks, namely {[Ln(BIPA-TC)_0.5(DMA)₂(NO₃)]·DMA·H₂O}_n (1-Ln, Ln = Eu, Dy, Sm, Nd) and {[Ln₂(BIPA-TC)_1.5(DMA)₃(H₂O)₂]·2DMA·2H₂O}_n (2-Ln, Ln = Eu, Dy, Sm, Nd), were successfully constructed via a solvent regulation strategy based on a π-electron rich tetra-carboxylate ligand (H₄BIPA-TC). 1-Ln shows a 4-connected lvt topology with the point symbol of {4²·8⁴}, but 2-Ln displays a new 4,4,6-connected wxk1 topology with the point symbol of {4³·8³}₄{4⁶·6⁶·8³}₂{8⁶}. The solid-state luminescence property and the microporous nature of Eu-MOFs (1-Eu and 2-Eu) indicate that they can potentially be used as luminescent sensors. Fluorescence measurements indicate that Fe³⁺ exhibits the quenching effect for 1-Eu with the quenching efficiency of 93.1%. 2-Eu is the first MOF sensor for Mg²⁺ with the lowest detection limit of 1.53 × 10⁻¹⁰ mol L⁻¹ and displays good recyclable capability. Simultaneously, in the presence of other metal ions (Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pd²⁺, Al³⁺, Cr³⁺and Fe³⁺), 2-Eu can maintain the selective sensing of Mg²⁺, indicating its potential for Mg²⁺ turn-on sensing.