Design of a heterometallic Zn/Ca-MOF decorated with alkoxy groups on the pore surface exhibiting high fluorescence sensing performance for Fe3+ and Cr2O72

A fluorescent heterometallic Zn/Ca-MOF sensor, named {[(CH3)2NH2]4[Ca2Zn4(L)4]·4DMF}n (1), has been designed based on a flexible ligand ((5,5′-(propanen-1,3-diyl)-bis(oxy)diisophthalic acid (H4L))) under solvothermal conditions. Compound 1 features a novel (4,8)-connected 3D architecture with the linear trinuclear cluster [CaZn2(COO)8] bridged by eight carboxylate groups from different organic ligands. The introduction of Ca2+ into the Zn-MOF effectively improves the thermal and water stability of the heterometallic Zn/Ca-MOF, which encouraged us to evaluate its fluorescence sensing performance. Consequently, compound 1 exhibits highly selective sensing of Fe3+ and Cr2O72− through a luminescence quenching mechanism. The corresponding quenching coefficient (Ksv) values are 4.36 × 103 M−1 for Fe3+ and 1.15 × 103 M−1 for Cr2O72−. The detection limits are estimated to be 18.8 μM for Fe3+ and 29.1 μM for Cr2O72−, which are lower than most reported sensors. Furthermore, the DFT theoretical calculation simulates the modified channel A of alkoxy groups as recognition sites to explain its recognition mechanism for Fe3+.