Crystal structures and syntheses of four novel Cu(I)-MOFs with in-situ reduced of Cu(II) and highly efficient fluorescent sensor for trace nitroaromatics

Abstract

Four novel Cu(I)-based metal-organic frameworks, [Cu3(p-IPIB)(CN)Cl2]n (Cu(I)-MOF-7), [Cu3(p-IPIB)(CN)Cl2]n (Cu(I)-MOF-8), [Cu3(p-IPIB)Cl3]n (Cu(I)-MOF-9) and [Cu2(p-IPIB-Cl)1/2Cl2(H2O)]n (Cu(I)-MOF-10) where ligand p-IPIB is 1,4-bis[(2-(4-(1H-imidazol -1-yl)-phenyl)-1H-imidazole-1-yl)-methyl]-benzene, have been successfully synthesized by in-situ reduction of Cu(II) under solvothermal reaction condition. Single X-ray diffraction analysis shown that Cu(I)-MOF-7 and 8 are not only structural supramolecular isomerism containing cyano-bridge which was in situ obtained from the cleavage of the CCN bond of acetonitrile solvent, but also a 3D twofold interpenetration metallo-supramolecular assembly for Cu(I)-MOF-7 and a 3D porous supramolecular assembly containing the macrometallacyclic box structure for Cu(I)-MOF-8, respectively. Cu(I)-MOF-9 is a 1D channel polymeric chain motif with macrometallacyclic structure containing [Cu3Cl3] cluster of μ3- and μ2-chloride bridge. And Cu(I)-MOF-10 is also a 3D twofold interpenetration metallo-supramolecular assembly with [Cu4Cl3(H2O)2] cluster of μ4-chloride bridge. They are thermally stable and exhibit apparent porous properties with adsorption of N2 and CO2 gas. The fluorescence sensing experiment indicated that Cu(I)-MOF 7–10 can be used for detecting nitroaromatic explosives through fluorescence quenching in the solution and they have the best sensing effects on the detection of 2,4,6-Trinitrophenol (TNP). Especially, Cu(I)-MOF-9 has the best sensing property towards TNP with a higher quenching constant of 4.53 × 104 L/mol and a lower detection limit of 1.21 ppm.