Two trinuclear cluster metal–organic frameworks: syntheses, structures, highly fluorescent sensing and magnetic properties

Abstract

Two new metal–organic frameworks [Zn3(TCPB)2(H2O)2]·3DMF·2H2O (1) and [Mn1.5(TCPB)(DMF)(H2O)]·DMF(2)(H3TCPB = 1,3,5-tri(4-carboxyphenoxy)benzene), have been successfully constructed by solvothermal methods and structurally characterized by single crystal X-ray diffraction, elemental analyses, IR spectra, Raman spectra, 1H NMR spectra, powder X-ray diffraction and thermogravimetric analyses. Single-crystal X-ray diffraction analyses reveal that complex 1 crystallizes in the trigonal space group P3¯ 1c and possesses a 2D network, whereas complex 2 crystallizes in the triclinic space group P1¯ and also possesses a 2D network. TOPOS analyses reveal that both complexes 1 and 2 have a (3,6)-connected network topology with the Schläfli symbol of (43·612) (43)2 for 1 and {43}2{46·66·83} for 2. Notably, further investigation indicates that complex 1 can be employed as a bi-functional fluorescent sensor for highly sensitive and selective detection of ferric ions (Fe3+) and 2,4,6-trinitrophenol (TNP), with the detection limit of 0.11 μM for Fe3+ and 0.14 μM for TNP. Furthermore, the possible fluorescence quenching mechanisms are explained as: (a) photo-induced electron transfer (PET) caused by the HOMO-LUMO energy gap through DFT and (b) fluorescence resonance energy transfer (FRET). Besides, the magnetic property measurement indicated that complex 2 shows antiferromagnetic interactions between trinuclear {Mn3(COO)6} SBUs.