A Photoluminescent Cd(II) Coordination Polymer with Potential Active Sites Exhibiting Multiresponsive Fluorescence Sensing for Trace Amounts of NACs and Fe3+ and Al3+ Ions.

The elaborately designed π-electron-rich fluorescent ligand 1,4-bis(1-carboxymethylene-4-imidazolyl)benzene (H2L), possessing bifunctional groups including the carboxylate groups (building units) and 4-imidazoyl groups (N-donor potential active sites) has been employed to construct fluorescent coordination polymers. A luminescent sensor, namely [Cd(L)(phen)2]·5H2O (1), was obtained, which has a one-dimensional structure. The fluorescent material shows a blue emission maximum at 457 nm with a luminescence lifetime of 488 ns and a quantum yield (QY) of 4.56%. Significantly, 1 serves as a promising multiresponsive luminescent sensor to detect trace nitroaromatic compounds (NACs) with the limits of detection (LOD) of 7.21 × 10-8, 1.85 × 10-5, and 1.15 × 10-5 mol/L for 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), and 4-nitrophenol (4-NP), respectively. Furthermore, CP 1 exhibits fluorescent turn-off and turn-on sensing behavior for Fe3+ and Al3+ metal ions with trace amounts of 1.05 × 10-7 and 1.13 × 10-7 mol/L, respectively. Experimental methods and theoretical calculations were employed to elucidate the sensing mechanism in detail.

Reversible single-crystal-to-single-crystal transformation and highly selective adsorption property of three-dimensional cobalt(II) frameworks.

A three-dimensional (3D) coordination polymer, [Co(3)(L)(2)(BTEC)(H(2)O)(2)]·2H(2)O [1, HL = 3,5-di(imidazol-1-yl)benzoic acid, H(4)BTEC = 1,2,4,5-benzenetetracarboxylic acid], with tfz-d topology has been hydrothermally synthesized. The framework of 1 has high thermal stability and exhibits single-crystal-to-single-crystal (SCSC) transformations upon removing and rebinding the noncoordinated and coordinated water molecules. X-ray crystallographic analyses revealed that the coordination geometry of Co(II) changes from octahedral to square pyramid upon dehydration, accompanying the appearance of one-dimensional (1D) open channels with dimensions of 2.0 × 2.8 Å. The dehydrated form [Co(3)(L)(2)(BTEC)] (2) exhibits highly selective adsorption of water molecules over N(2), CH(3)OH, and CH(3)CH(2)OH, which could be used as sensors for water molecules. Furthermore, the magnetic properties of 1 and 2 were investigated, showing the existence of ferromagnetic interaction between the Co(II) atoms within the trinuclear subunit.

catena-Poly[[aqua-[1,4-bis-(1H-imidazol-4-yl)benzene]cadmium]-µ(3)-5-methyl-isophthalato].

In the title coordination polymer, [Cd(C(9)H(6)O(4))(C(12)H(10)N(4))(H(2)O)](n), the Cd(II) atom has a NO(6) donor set and is coord-inated by five carboxyl-ate O atoms from three different 5-methyl-1,3-phenyl-enediacetate (pda(2-)) anions, one O atom from a water mol-ecule and one N atom from a 1,4-bis-(1H-imidazol-4-yl)benzene (L) ligand, displaying a highly distorted penta-gonal-bipyramidal geometry. Each pda(2-) anion acts as a µ(3)-bridge, linking Cd(II) atoms to form one-dimensional slabs extending parallel to [010]. In the crystal, adjacent mol-ecules are linked through N-H⋯N and N-H⋯O hydrogen bonds into a three-dimensional network.

Poly[[µ-1,4-bis-(1H-imidazol-4-yl)benzene-κN:N](µ-5-methyl-isophthalato-κO:O)cobalt(II)].

In the title coordination polymer, [Co(C(9)H(6)O(4))(C(12)H(10)N(4))](n), the Co(II) atom is four-coordinated by two O atoms from two different 5-methyl-isophthalate bivalent anions and two N atoms from two different 1,4-bis-(1H-imidazol-4-yl)benzene ligands, forming a four-coordinated tetra-hedral coordination geometry. Each 5-methyl-isophthalate ligand acts as a µ(2)-bridge, linking two Co(II) atoms and forming chains which are further linked by 1,4-bis-(1H-imidazol-4-yl)benzene ligands into a two-dimensional network parallel to ([Formula: see text]01). These planes are, in turn, linked by two inter-molecular N-H⋯O inter-actions, forming a three-dimensional structure. Weak C-H⋯O hydrogen bonds are also present in the structure.

Poly[bis-[µ-1,4-bis-(1H-imidazol-5-yl)benzene-κN:N]diformatomanganese(II)].

In the title compound, [Mn(CHO(2))(2)(C(12)H(10)N(4))(2)](n), the Mn(II) atom and the benzene ring of the ligand lie on an inversion centers. The Mn(II) atom has an octa-hedral coordination environment composed of four N atoms from two different symmetry-related N-heterocyclic ligands forming the basal plane, and two O atoms from symmetry-related formate anions occupying the apical positions. The title compound forms a two-dimensional (4,4) net parallel to (100) with all the Mn(II) atoms lying on a plane. The crystal structure is consolidated by inter-molecular N-H⋯O hydrogen bonds..

A Fluorescent and Colorimetric Chemosensor for Hg2+ Based on Rhodamine 6G With a Two-Step Reaction Mechanism.

A fluorescent and colorimetric chemosensor L based on rhodamine 6G was designed, synthesized, and characterized. Based on a two-step reaction, the chemosensor L effectively recognized Hg2+. The interaction between the chemosensor and Hg2+ was confirmed by ultraviolet-visible spectrophotometry, fluorescence spectroscopy, electrospray ionization-mass spectrometry, Fourier-transform infrared spectroscopy, and frontier molecular orbital calculations. The chemosensor L was also incorporated into test strips and silica gel plates, which demonstrated good selectivity and high sensitivity for Hg2+.

Using Smartphone APP To Determine the CN- Concentration Quantitatively in Tap Water: Synthesis of the Naked-Eye Colorimetric Chemosensor for CN- and Ni2+ Based on Benzothiazole.

A naked-eye colorimetric chemosensor DK based on benzothiazole could recognize CN- effectively. When DK interacted with CN- in the aqueous solution, the obvious color change of the solution was directly observed by the naked eye. Other anions did not cause any interference. It is interesting that DK could also discriminate Ni2+ from other cations, and the possible interaction mode between them was verified based on the Job's plot, 1H nuclear magnetic resonance titration, infrared , electrospray ionization mass spectrometry, scanning electron microscopy analysis, and density functional theory calculation methods. As a result, it is clear that the mode of action between DK and CN- was different from that between DK and Ni2+. Meanwhile, the limit of detection of DK toward CN- and Ni2+ was calculated to be 1.7 × 10-8 or 7.4 × 10-9 M, respectively. In addition, CN- was recognized qualitatively by a test paper and silica gel plates made from DK. DK was able to detect CN- in tap water quantitatively, rapidly, and on-site by the use of a smartphone APP. All results implied that DK has certain prospects for practical application to identify CN- in water.

Series of Cadmium(II) Coordination Polymers Based on a Versatile Multi-N-Donor Tecton or Mixed Carboxylate Ligands: Synthesis, Structure, and Selectively Sensing Property.

Five Cd(II) metal-organic frameworks (MOFs), [Cd(HL)2] (1), [Cd(HL)2(H2O)2] (2), [Cd3(HL)2(obda)2] (3), [Cd2(HL)2(ohmbda)(DMA)(H2O)] (4), and [Cd2(HL)(btc)(H2O)2]·3H2O (5), were prepared by reactions of Cd(NO3)2·4H2O with 1-(1H-imidazol-4-yl)-4-(4H-tetrazol-5-yl)benzene (H2L) or mixed carboxylate ancillary ligands of 1,2-benzenedicarboxylic acid (H2obda), 5-hydroxy-1,3-benzenedicarboxylic acid (H2ohmbda), and 1,3,5-benzenetricarboxylic acid (H3btc), respectively. Their structures have been characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy (IR), thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 and 2 are supramolecular isomeric frameworks without consideration of the solvent molecules. Complex 1 exhibits a binodal (3, 5)-connected two-dimensional (2D) layer structure with the point (Schläfli) symbol of (52·6)(55·64·7), while complex 2 shows a 2D + 2D → 3D (three-dimensional) framework. Complex 3 is a (3, 5, 6)-connected tetranodal 3D net with the point (Schläfli) symbol of (4·82)2(45·6·84)2(45·65)2(48·66·8). Compound 4 is a (3, 3, 8)-connected trinodal 3D net with the point (Schläfli) symbol based on a binuclear [Cd2N2O] subunit, while 5 is a 2-nodal (3, 4)-connected 2D V2O5-type network based on [Cd2N2(COO)2] SBU. The studies of molecular sensing properties show that the luminescent MOFs can be employed as fluorescent sensors for the detection of Fe3+ and nitro compounds. Compound 1 and 3 exhibit quenching responses for Fe3+ in dimethylformamide solution with detection limits of 2.3 × 10-6 and 8.6 × 10-7 M, respectively. Meanwhile, compound 5 can sense 4-nitrophenol with a detection limit as low as 5.75 × 10-7 M.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate.

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu2+ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH3CN (40:60, V/V). The detection limit of WM toward Cu2+ was 1.84 × 10-7 M, which was lower than the concentration of Cu2+ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu2+ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu2+.

Long-Wavelength Fluorescent Chemosensors for Hg2+ based on Pyrene.

A novel long-wavelength turn-on fluorescent chemosensor CS based on pyrene was synthesized to detect Hg2+. In the presence of other metal ions, CS could effectively recognize Hg2+ and produce the turn-on fluorescent emission at 607 nm. Also, the absorption spectrum exhibited red-shift. Meanwhile, the change of the solution color from yellow to orange was directly observed by the naked eye. The interaction between CS and Hg2+ was confirmed by the Job's plot, electrospray ionization mass spectrometry, scanning electron microscopy, and density functional theory calculations. It was found that the fluorescence of CS could be reversible when I- was added into the solution of CS and Hg2+. CS illustrated high selectivity and good sensitivity for Hg2+ with the limit of detection of 36 nm. Moreover, CS could be utilized as test strips and silica gel plates to identify Hg2+.

Metal(II) Coordination Polymers Derived from Mixed 4-Imidazole Ligands and Carboxylates: Syntheses, Topological Structures, and Properties.

Four new metal⁻organic coordination polymers [Cu(L)(mpa)]·3H2O (1), [Co(L)(mpa)]·H2O (2), [Zn(L)(mpa)]·H2O (3), and [Cd(L)(mpa)(H2O)]·H2O (4) were synthesized by reactions of the corresponding metal(II) salts based on mixed ligands of 1,4-di(1H-imidazol-4-yl)benzene (L) and 4-methylphthalic acid (H2mpa), respectively. The structures of the complexes were characterized by elemental analysis, FT-IR spectroscopy, and single-crystal X-ray diffraction. Compound 1 exhibits a binodal 4-connected three dimensional (3D) architecture with (65·8)-CdSO4 topology, while complexes 2 and 3 are isostructural and have two-dimensional (2D) layer structure with (4, 4) sql topology based on the binuclear metal subunits. Complex 4 has the same 2D layer structure with (4, 4) sql topology as complexes 2 and 3, but the inclined interpenetration of parallel sets of layers result in the formation with 2D + 2D → 3D framework. The activated sample 1 shows selective CO2 uptake over N2. The photoluminiscent properties together with quantum yield (QY) and luminescence lifetime are also investigated for complexes 3 and 4 in the solid state at room temperature.

A highly selective and reversible fluorescence "OFF-ON-OFF" chemosensor for Hg2+ based on rhodamine-6G dyes derivative and its application as a molecular logic gate.

A new rhodamine-6G-based chemosensor X was designed and synthesized for the colorimetric and fluorometric detection of Hg2+. The chemosensor X responsed to Hg2+ had good sensitivity, high selectivity and excellent reversibility in HEPES buffer (10 mM, pH 7.4)/CH3CN (40:60, V/V). The recognition mechanism of X toward Hg2+ was evaluated by Job's plot, IR and MS. Meanwhile, X-Hg2+ fluorescence lifetime was also measured. It was interesting that X displayed favorable reversibility to form an "off-on-off" type signaling behavior with the Hg2+-induced emission spectra being quenched by I-. Furthermore, it could be applied as a molecular logic gate and test strips based on X exhibited a good reversibility selectivity to Hg2+.

Zinc(II) and cadmium(II) metal-organic frameworks with 4-imidazole containing tripodal ligand: sorption and anion exchange properties.

The use of a 4-imidazole containing tripodal ligand 1,3,5-tri(1H-imidazol-4-yl)benzene (H3L) enabled isolation of two three-dimensional (3D) porous metal-organic frameworks (MOFs) [Zn(HL)] · solvent (1) and [Cd(H3L)2](ClO4)2 · 10.5H2O (2) featuring 4,4- and 3,6-connected nets related to the structures of ecl and pyrite, respectively. Framework 1 has 3D channels based on Zn-Im(-) (Im(-) = imidazolate) moieties due to partial deprotonation of the 1H-imidazol-4-yl groups of H3L while porous framework 2 is constructed by the coordination of neutral H3L ligands with Cd(II). Desolvated solid 1' showed remarkable uptake for CO2, N2, H2, CH4 gases as well as the volatile organic vapor of MeOH, EtOH, i-PrOH and C6H6, significantly, exhibiting temperature dependent selective gas sorption for CO2 over N2. Grand Canonical Monte Carlo (GCMC) simulations were performed to elucidate the mechanism of the selective gas adsorption. Cage-like motifs are found in pyrite-net 2, in which ClO4(-) anions are hosted, and the results of IR, elemental analysis and PXRD measurements confirm that 2 has a reversible anion exchange property among perchlorate, nitrate and nitrite anions.

Determination of nitrofuran metabolites in shrimp by high performance liquid chromatography with fluorescence detection and liquid chromatography-tandem mass spectrometry using a new derivatization reagent.

A high performance liquid chromatography with fluorescence detection (HPLC-FLD) method for the simultaneous determination of total nitrofuran metabolite residues (furazolidone, furaltadone, nitrofurantoin, and nitrofurazone) in shrimp was developed. The method involves the acid hydrolysis of protein-bound metabolites, followed by the derivatization of the freed metabolites with the new fluorescent derivatization reagent 2-hydroxy-1-naphthaldehyde (HN) and subsequent liquid-liquid extraction (LLE). Separation is achieved on a YMC-Pack Polymer C18 column under alkaline conditions, and the high fluorescence intensity of the derivatives at an emission wavelength Em=463nm (Ex=395nm) enables, for the first time, their simultaneous determination in shrimp at concentrations as low as 1µg/kg by HPLC-FLD. The method was validated using blank shrimp fortified with all four metabolites at 0.5, 1.0 and 2.0µg/kg. Recoveries were >87% with relative standard deviations of <8.1% for all four metabolites. Furthermore, the results obtained by HPLC-FLD were in very good agreement with those obtained by LC-MS/MS analysis.

High-performance liquid chromatography with fluorescence detection for the determination of nitrofuran metabolites in pork muscle.

A simple and sensitive HPLC method with fluorescence detection (HPLC-FLD) is reported for the simultaneous determination of metabolites of four nitrofuran drugs (furazolidone, furaltadone, nitrofurantoin and nitrofurazone) in pork muscle. The method involves acid hydrolysis of the protein-bound drug metabolites and the conjugation of the released side-chains with a novel fluorescence agent 2-hydroxy-1-naphthaldehyde. After liquid-liquid extraction and effective separation of the derivatives on a YMC-Pack Polymer C18 column at 40°C under alkaline conditions, the high fluorescence intensity of these derivatives at emission wavelength λem = 463 nm enables their simultaneous determination in pork muscle at concentrations as low as 1 µg kg⁻¹. The method was validated using blank pork muscle fortified with all four metabolites at 0.5, 1.0 and 2.0 µg kg⁻¹. Recoveries were > 92.3% with RSDs < 8.5% for all four metabolites. The results obtained with HPLC-FLD and LC-MS/MS methods showed very good agreement for pork muscle samples.

Temperature dependent selective gas sorption of the microporous metal-imidazolate framework [Cu(L)] [H2L = 1,4-di(1H-imidazol-4-yl)benzene].

A highly stable copper(II) microporous framework with cylindrical channels constructed from 1,4-di(1H-imidazol-4-yl)benzene (H(2)L) and CuCl(2)·2H(2)O is composed of Cu(II)-imidazolate tubes interconnected by the 1,4-phenylene group of L(2-), and shows temperature dependent selective gas sorption properties.

Porous cobalt(II)-imidazolate supramolecular isomeric frameworks with selective gas sorption property.

Two porous supramolecular isomeric frameworks show unique sorption properties, one with temperature dependent stepwise and hysteretic selective sorption of CO(2) while the other one shows gas uptake capacity for CO(2), N(2), H(2) and CH(4) at low temperature and selective sorption of CO(2) over N(2) around room temperature.