Fei-Long Hu

A unique Zn(II)-based MOF fluorescent probe for the dual detection of nitroaromatics and ketones in water

We herein report a fluorescent Zn(II)-supported metal–organic framework (MOF) [Zn4(Hbpvp)2(BTC)3(HCOO)(H2O)2]·4H2O (1) (bpvp = 3,5-bis-(2-(pyridin-4-yl)vinyl)pyridine; H3BTC = 1,3,5-benzenetricarboxylic acid) assembled from solvothermal reactions of ZnSO4·7H2O with bpvp and H3BTC ligands. Compound 1 has a unique two-dimensional (2D) layer structure and exhibits a high sensitivity and a low limit of detection of 1.0 × 10−6 mol L−1 for both 2,4-dinitrophenol (2,4-DNP) and p-benzoquinone (p-BQ) in aqueous solutions, inferred from fluorescence quenching studies. The fluorescent intensity of 1 recovers upon removal of analytes, making it a promising recyclable dual-targeted luminescent probe for 2,4-DNP and p-BQ in water.

Ligand geometry-directed assembly of seven entangled coordination polymers

Seven new complexes [Cd(oba)(2,2′-bipy)]2 (1), [Co(oba)(bbm)]·1.5H2O (2), [Mn3(oba)3(bbm)(H2O)2]·DMF·2H2O (3), [Mn2(bibm)2(oba)2] (4), [Co(oba)(bibm)]2·H2O (5), [Co5(bpb)3(oba)4(Hoba)2(H2O)2] (6) and [Ni2(bpb)2(oba)2(DMF)(H2O)]2·5H2O (7) (H2oba = 4,4′-oxydibenzoic acid, bbm = 1,4-di(1H-imidazol-1-yl)benzene, bibm = 4,4′-di(1H-imidazol-1-yl)-1,1′-biphenyl, bpb = 1,4-di(pyridin-4-yl)benzene, 2,2′-bipy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, X-ray powder diffraction and X-ray single crystal diffraction. Compound 1 displays a 3-fold polythreaded 2D network, while 2 has sql layers and these layers are further stacked in a 2D → 3D polycatenation model. Compound 3 shows a 3D porous net with {421·54·63} topology with 1D channels that are filled by DMF and water molecules while 4 possesses a 2D (4,4) layer structure composed of [Mn2(bibm)2(oba)2] units. Compound 5 exhibits a five-fold interpenetrating 3D framework while 6 displays a 2D → 3D polycatenation motif. Compound 7 has a three-fold interpenetrating 3D framework. These results provide some insight into the ligand geometry-driven assembly of entangled coordination polymers. Thermal stability and photoluminescence properties of 1–7 were studied. The optical and photocatalytic properties of 3 and 6 were also investigated.

In-situ X-ray diffraction snapshotting: determination of the kinetics of a photodimerization within a single crystal.

In a single-crystal-to-single-crystal (SCSC) transformation, a preformed three-dimensional coordination polymer,[Ni3(oba)2(bpe)2(SO4)(H2O)4]·H2O (H2oba = 4,4′-oxydibenzoic acid; bpe = (E)-1,2-di(pyridin-4-yl)ethane) (1), was shown to undergo a [2+2] cycloaddition reaction upon exposure to UV irradiation. The kinetics of this reaction were followed by taking “snapshots” of the solid state transformation using in situ single crystal X-ray crystallography; a first order process was indicated. The reaction rate was influenced by many factors such as the separation of the sample from the UV light source, the heat produced by the UV irradiation, the light flux of the UV lamp used, the size of the single-crystal and the powder samples. The investigation of the kinetics was complemented by 1H NMR studies. The results clearly demonstrate that in situ single-crystal X-ray diffraction is able to provide useful insights into the gradual formation of the photoproducts and the reaction processes. The work also offers a clear indication that it is possible to use the technique to study the kinetics of other photocycloaddition reactions and SCSC processes in general.

Observance of a large conformational change associated with the rotation of the naphthyl groups during the photodimerization of criss-cross aligned CC bonds within a 2D coordination polymer

Five coordination polymers [Zn(oba)(4-spy)]2·(4-spy)0.25·(H2O) (1), [Zn2(oba)2(HT-ppcb)]2·(4-spy)0.25 (1a), [Zn(oba)(4-(2-npy))]2·(4-(2-npy))0.25·(H2O)1.25 (2), [Zn(oba)(4-npy)]2·(4-npy)0.25 (3) and [Zn2(oba)2(HT-pncb)]· (4-npy)0.25 (3a) (H2oba = 4,4′-oxydibenzoic acid; 4-spy = (E)-4-styrylpyridine; HT-ppcb = 1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane; 4-(2-npy) = (E)-4-(2-(naphthalen-2-yl)vinyl)pyridine; 4-npy = (E)-4-(2-(naphthalen-1-yl)vinyl)pyridine; HT-pncb = rctt-1,3-bis(4-pyridyl)-2,4-bis(1-naphthyl)cyclobutane) were structurally determined. In each case, pairs of Zn(II) centres are linked by oba2− anions to form a 2D network. Olefinic pyridyl ligands bound to Zn(II) extend above and below the mean plane of the network and are located within the windows of adjacent parallel networks. Each window contains a pair of vinyl-pyridyl ligands that are tethered to networks that lie above and below and arranged in a head-to-tail manner. 1–3 show different alignments of the CC bond pair achieved by introducing olefinic ligands with different sizes of their terminal groups. In 1, the CC bonds are parallel and close enough for a [2 + 2] cycloaddition reaction to occur upon exposure to UV light. The CC bonds in 2 are too far apart to combine and no reaction occurs upon UV irradiation. In 3, the CC bonds are less than 4.0 A apart and has a criss-cross arrangement. Exposure of 3 to UV light leads to a [2 + 2] cycloaddition reaction. Analysis of the “before” and “after” structures shows a large conformational change associated with the rotation of the olefinic bonds and/or the naphthyl groups when the photodimerization of criss-cross CC bonds is undergone.

Efficient ring-opening polymerization (ROP) of ε-caprolactone catalysed by isomeric pyridyl β-diketonate iron(iii) complexes

A series of Fe(III) complexes of β-diketonate ligands, 1-(2-pyridyl)-3-(3-pyridyl)-1,3-propanedione (L1), 1-(2-pyridyl)-3-(2-pyridyl)-1,3-propanedione (L2), 1-(2-pyridyl)-3-(4-pyridyl)-1,3-propanedione (L3), 1-(3-pyridyl)-3-(4-pyridyl)-1,3-propanedione (L4), 1-(3-pyridyl)-3-(3-pyridyl)-1,3-propanedione (L5) and 1-(4-pyridyl)-3-(4-pyridyl)-1,3-propanedione (L6), viz. [Fe(L1)3] (1), [Fe(L2)3] (2), [Fe(L3)3] (3), [Fe(L4)3] (4), [Fe(L5)3] (5) and [Fe(L6)3] (6) have been structurally characterized. All but one complex (1) catalyzed the ring-opening polymerization (ROP) of e-caprolactone (e-CL) in near quantitative yield at 110 °C to give polymers with relatively narrow polydispersities (PDI). The comparison of in situ reaction and a reaction with preformed 1 indicated that the latter was a better catalyst, giving a higher molecular weight. Complex 2 catalyzed this reaction in a more modest yield reflecting its greater thermal stability, shorter Fe–O bonds and minimal distortion in fold angle among the isomeric complexes, suggesting that ligand dissociation is important for catalytic activity.

A pyrazolopyrimidine based fluorescent probe for the detection of Cu2+ and Ni2+ and its application in living cells

A fluorescent sensor L based on a pyrazolopyrimidine core simultaneously detects Cu2+ and Ni2+ ions by photoluminescence quenching, even in the presence of other metal cations. Sensor L possesses high association constants of 5.24 × 103 M-1 and 2.85 × 104 M-1 and low detection limits of 0.043 μM and 0.038 μM for Cu2+ and Ni2+, respectively. The binding stoichiometry ratios of L to Cu2+ or Ni2+ is 1:1 as determined by Benesi-Hildebrand and Jobs plots, and by crystal structures. DFT calculations on L-Cu2+ indicated reduced electron donation from the coordinated pyrazolopyridine to the fused pyrimidine and pendant phenyl group which, together with a smaller HOMO-LUMO orbital gap could favour non-radiative decay and explain the observed fluorescence quenching. Sensor L possessed low cytotoxicity and good imaging characteristics for Cu2+ and Ni2+ in living cells, suggesting potential applications for detecting Cu2+ and Ni2+in vivo.