Two magnesium based metal-organic frameworks (Mg-MOFs): Structures, photochromism, and fluorescence sensing to Fe3+ ions and cysteine molecules

Abstract

Here in this work, two magnesium based metal organic frameworks (Mg-MOFs) assembled from 1,4-naphthalinic acid (1,4-H2NDC) and pyridine-containing ligands of 1,2-di(4-pyridyl)ethylene (L1) or 2-di(pyridin-4-yl)diazene (L2) are presented and characterized. In these two compounds, L1 or L2 act as the terminal ligands coordinated to the Mg 2+ ions in the binuclear second building units (SBUs) to generate two-dimensional (2D) [Mg2(1,4-NDC)4(H2O)(L)]•H2O networks (where L=L1 for 1 and L=L2 for 2). Although compounds 1 and 2 are constructed from ligands that are not intrinsically photoactive, both compounds exhibit photochromic behavior, representing the first reported two-dimensional (2D) photochromic Mg-MOFs achieved from coordination between Mg 2+ and the non-photochromic organic ligands. Moreover, compound 1 displays a bright blue fluorescence and can function as a selective fluorescent sensing material towards Fe 3+ ions. When modified with CuI, it exhibits dual-emission and shows fluorescence sensing ability to Cysteine (Cys) molecule as well. This work provides a useful reference for designing fluorescent sensing MOFs using earth-abundant metals.