Solvent-induced terbium metal–organic frameworks for highly selective detection of manganese(ii) ions

Abstract

Highly selective detection of trace metal ions has become one of the most urgent issues in public security and living systems. Developing a highly efficient fluorescent sensor for manganese(II) (Mn²⁺) ions is a huge challenge. Herein, by utilizing the solvent regulation approach, a pair of terbium metal–organic frameworks (UPC-36, [Tb₂(btdc)₃(DMF)(H₂O)₄]·DMF and UPC-37, [Tb₂(btdc)₃(H₂O)₆]) based on a π-electron-rich ligand (H₂btdc = 2,2′-bithiophene-5,5′-dicarboxylic acid) has been chosen as highly efficient sensors for the selective detection of Mn²⁺ ions. Interestingly, the fluorescence of UPC-36 can be quenched by Mn²⁺, Cu²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions, while UPC-37 can only be quenched by Mn²⁺ ions. For detecting Mn²⁺ ions, the limit of detection (LOD) values are calculated to be 0.813 mM and 0.715 mM for UPC-36 and UPC-37 respectively. According to the ICP results, UPC-37 has stronger interactions with Mn²⁺ ions because of the more regular arrangement of ligands existing in UPC-37, so it exhibits a high sensitivity and selectivity (K_sv = 5.25 × 10⁵ M⁻¹).