Aggregation-Induced Emission Phosphorescence Featured Au-Ag Coordination Polymer with a Diphosphine N-Heterocyclic Carbene Ligand for Highly Sensitive Detection of Cr(VI).

Luminescent materials with aggregation-induced emission (AIE) characteristics have been recognized as highly selective and sensitive probes for the detection of toxic metal ions in recent years. In this paper, a Au-Ag cluster-based coordination polymer [Au3Ag3(L)2(CN)6(H2O)2]n [1, L = 1,3-bis((diphenylphosphanyl)methyl)-4,5-dihydro-imidazolylidene] was prepared by in situ generation of the diphosphine N-heterocyclic carbene (PCNHCP)-type ligand L in the presence of the corresponding metal salts. Compound 1 exhibited 530 nm phosphorescence under 380 nm excitation with a QY of 6.30% and a lifetime (τ) of 7.14 µs in the solid state. 1 showed good AIE behavior in the mixture of MeOH/H2O while the best aggregation state (fwater = 90%, QY = 6.79%, τ = 6.70 µs) exhibited selective and sensitive emission quenching toward Cr(VI) ions. Ultralow detection limits of 9.7 ppb (w/w) for Cr2O72- and 17.9 ppb (w/w) for CrO42- were achieved.

One-Dimensional Heterobimetallic Au/Ag Coordination Polymer Showing a Selective, Reversible, and Visible Vapor-Chromic Photoluminescent Response toward Methanol.

A heterobimetallic coordination polymer [Au4(dppmt)4(AgCl)2]n (1) incorporating an in situ generated P-S ligand (dppmtH) was synthesized from the solvothermal reaction of Au(tht)Cl, AgCl, and dpppyatc in CH3CN/CH2Cl2 (dppmtH = (diphenylphosphino)methanethiol, tht = tetrahydrothiophene, dpppyatc = N,N-bis((diphenylphosphaneyl)methyl)-N-(pyridin-2-yl)-amino-thiocarbamide). The structure of 1 contains a one-dimensional helical Au-Au chain in which the unique [Au4Ag2S2] cluster units are connected by [Au2(dppmt)2] dimers. Upon excitation at 343 nm, 1 exhibited cyan (495 nm) phosphorescent emission at quantum yield (QY) = 22.3% and τ = 0.78 µs (λex = 375 nm). Coordination polymer 1 exhibited a rapid, selective, reversible, and visible vapor-chromic response on exposure to methanol (MeOH) vapor with its emission shifting to a more intense green (530 nm, λex = 388 nm) with QY = 46.8% and τ = 1.24 µs (λex = 375 nm). A polymethylmethacrylate film containing 1 served as a reversible chemical sensor for the sensitive detection of MeOH in air.

Silver(I) Coordination Polymer Ligated by Bipyrazole Me4bpzH2, [Ag(X)(Me4bpzH2)] (X = CF3CO2- and CF3SO3-, Me4bpzH2 = 3,3',5,5'-Tetramethyl-4,4'-bipyrazole): Anion Dependent Structures and Photoluminescence Properties.

Coordination polymers of transition metal ions are fascinating and important to coordination chemistry. One of the ligands known to form particularly interesting coordination polymers is 3,3',5,5'-tetramethyl-4,4'-bipyrazole (Me4bpzH2). Group 11 metal(I) ion coordination polymers, other than those of copper(I), are relatively easy to handle because of their low reactivity towards dioxygen and moisture. However, the known silver(I) coordination polymers often have poor solubility in common solvents and so cannot be easily analyzed in solution. By using a tetramethyl substituted bipyrazole ligand, we have synthesized more soluble silver(I) complexes that contain the trifluoromethyl group in the coordinated ions CF3CO2- and CF3SO3- in [Ag(CF3CO2)(Me4bpzH2)] and [Ag(CF3SO3)(Me4bpzH2)]. We determined both structures by single-crystal X-ray analysis at low temperatures and compared them in detail. Moreover, we investigated the solution behavior of these coordination polymers by 1H-NMR, IR, Raman, UV-Vis spectroscopies, and their low-temperature, solid-state photoluminescence. The high-energy band at ~330 nm corresponded to ligand-centered (bipyrazole) fluorescence, and the low-energy band at ~400 nm to ligand-centered phosphorescence resulting from the heavy atom effect.

A Novel Photoluminescent Ag/Cu Cluster Exhibits a Chromic Photoluminescence Response towards Volatile Organic Vapors.

A new Ag/Cu bimetallic cluster [Ag10Cu6(bdppthi)2(C≡CPh)12(EtOH)2](ClO4)4 (1, bdppthi = N,N'-bis(diphenylphosphanylmethyl)-tetrahydroimidazole) exhibited strong phosphorescent (PL) emission at 644 nm upon excitation at 400 nm. Removal of the coordinated EtOH molecules in 1 resulted in derivative 1a, which exhibited significant red-shifted emission at 678 nm. The structure and PL of 1 was restored on exposure to EtOH vapor. Cluster 1a also exhibited a vapor-chromic PL response towards other common organic solvent vapors including acetone, MeOH and MeCN. A PMMA film of 1a was developed as a reusable visible sensor for MeCN.

A Multiple Stimuli-Responsive Ag/P/S Complex Showing Solvochromic and Mechanochromic Photoluminescence.

The reaction of CF3COOAg, 3-bdppmapy (N,N-bis(diphenylphosphanylmethyl)-3-aminopyridine) and HTZ (1,2,4-triazole-3-thiol) in CH2Cl2/MeOH resulted in a dinuclear Ag/P/S complex [Ag2(TZ)2(3-bdppmapy)2]·xSol (1·xSol). Crystals of 1·xSol converted to 1·2MeOH in air at room temperature and further to 1 under vacuum upon heating. The solid-state, room-temperature photoluminescent emission of 1·xSol (510 nm) shifted to 494 nm (1·2MeOH) and 486 nm (1). Grinding solids of 1·2MeOH in air resulted in amorphous 1G characterized by solid-state emission at 468 nm, which converted to 1GR with 513 nm emission upon MeOH treatment. Grinding 1GR in air returned 1G, and this interconversion was reproducible over five cycles. The solid-state photoluminescence of 1G changed in response to vapors containing low-molecular weight alcohols but remained unchanged after exposure to other volatile organic compounds (VOCs) or to water vapor. Test papers impregnated with 1G could detect methanol in vapors from aqueous solutions at concentrations above 50%. Complex 1G is, therefore, an example of a stimuli-responsive molecular sensor for the detection of alcohols.

Nanoscale Two-Dimensional FeII- and CoII-Based Metal-Organic Frameworks of Porphyrin Ligand for the Photodynamic Therapy of Breast Cancer.

The delivery of biocompatible reagents into cancer cells can elicit an anticancer effect by taking advantage of the unique characteristics of the tumor microenvironment (TME). In this work, we report that nanoscale two-dimensional FeII- and CoII-based metal-organic frameworks (NMOFs) of porphyrin ligand meso-tetrakis (6-(hydroxymethyl) pyridin-3-yl) porphyrin (THPP) can catalyze the generation of hydroxyl radicals (•OH) and O2 in the presence of H2O2 that is overexpressed in the TME. Photodynamic therapy consumes the generated O2 to produce a singlet oxygen (1O2). Both •OH and 1O2 are reactive oxygen species (ROS) that inhibit cancer cell proliferation. The FeII- and CoII-based NMOFs were non-toxic in the dark but cytotoxic when irradiated with 660 nm light. This preliminary work points to the potential of porphyrin-based ligands of transition metals as anticancer drugs by synergizing different therapeutic modalities.

Coordination Polymer-Mediated Molecular Surgery for Precise Interconversion of Dicyclobutane Compounds.

A Cd(II)-based coordination polymer {[Cd2(5-F-1,3-bpeb)2(FBA)4]·H2O}n (CP1) was obtained from Cd(II) salt, 5-fluoro-1,3-bis[2-(4-pyridyl)ethenyl]benzene (5-F-1,3-bpeb), and p-fluorobenzoic acid (HFBA). Within the one-dimensional chain structure of CP1, a pair of 5-F-1,3-bpeb was arranged in a face-to-face style. Upon UV irradiation and heat treatment, multiple cyclobutane isomers, including specific monocyclobutanes (1 with an endo-cyclobutane ring in CP1-1 and 1' with an exo-cyclobutane ring in CP1-1') and dicyclobutanes (endo,endo-dicyclobutane 2α in CP1-2α, exo,endo-dicyclobutane 2ß in CP1-2ß, and exo,exo-dicyclobutane 2γ in CP1-2γ) were stereoselectively produced. These isomers could be interconverted inside the CP via cutting/coupling specific bonds, which may be regarded as a type of molecular surgery. The precision of cutting/coupling relied on the thermal stability of the cyclobutanes and the alignment of the reactive alkene centers. The conversion processes were tracked through nuclear magnetic resonance, in situ powder X-ray diffraction, and IR spectroscopy. This approach can be considered as skeletal editing to construct complex organic compounds directly from one precursor.

Real-Time Monitoring of Surface Effects on the Oxygen Reduction Reaction Mechanism for Aprotic Na-O2 Batteries.

Discharging of aprotic sodium-oxygen (Na-O2) batteries is driven by the cathodic oxygen reduction reaction in the presence of sodium cations (Na+-ORR). However, the mechanism of aprotic Na+-ORR remains ambiguous and is system dependent. In-situ electrochemical Raman spectroscopy has been employed to study the aprotic Na+-ORR processes at three atomically ordered Au(hkl) single-crystal surfaces for the first time, and the structure-intermediates/mechanism relationship has been identified at a molecular level. Direct spectroscopic evidence of superoxide on Au(110) and peroxide on Au(100) and Au(111) as intermediates/products has been obtained. Combining these experimental results with theoretical simulation has revealed that the surface effect of Au(hkl) electrodes on aprotic Na+-ORR activity is mainly caused by the different adsorption of Na+ and O2. This work enhances our understanding of aprotic Na+-ORR on Au(hkl) surfaces and provides further guidance for the design of improved Na-O2 batteries.

Reversible Solid-State Phase Transitions between Au-P Complexes Accompanied by Switchable Fluorescence.

Six complexes {(3-bdppmapy)(AuCl)2}n (1-6; 3-bdppmapy = N,N'-bis(diphenylphosphanylmethyl)-3-aminopyridine and tht = tetrahydrothiophene) were simultaneously formed by the reaction of Au(tht)Cl and 3-bdppmapy in CH2Cl2 followed by infusion with hexane. Complexes 4-6 could be produced independently by volatilizing solvent in air, solid-state heating, or solvothermal reaction. The PPh2-Au-Cl moieties extended in different directions, forming Au-Au and Au-Au-Au interactions. Complex 4 could be converted to 5 by heating to 130 °C, with the cleavage of one Au-Au bond, while 5 reverted back to 4 upon exposure to CH2Cl2 vapor over 11 h. This solid-state phase transition could be recycled and was accompanied by a change in solid-state fluorescence, without obvious intensity decay over five cycles. The reason for both the phase transition and difference in photoluminescence is related to the different numbers and strengths of aurophilic interactions in each complex that could be modeled by density functional theory calculations.

Cobalt(II) and Nickel(II) Complexes of a PNN Type Ligand as Photoenhanced Electrocatalysts for the Hydrogen Evolution Reaction.

Hydrogen will be an important energy vector of the future, and improved efficiency in electrohydrolysis will accelerate this transition. In a fundamental study, we have prepared Co(II) and Ni(II) complexes of a new PNN type ligand N-((diphenylphosphanyl)methyl)-2-amino-1,10-phenanthroline (dppmaphen) incorporating the photoactive 1,10-phenanthroline group and the strongly coordinating diphenylphosphine to obtain photoelectrochemical (PEC) catalysts [Co(dppmaphen)2(NO3)2] (1) and [Ni(dppmaphen)2Cl]Cl (2) which catalyzed the hydrogen evolution reaction (HER) in alkaline media (1 M KOH). Overpotentials (η10) of 430 (1) and 364 mV (2) could be reduced to 345 (1) and 284 mV (2) under Xe light irradiation. This irradiation generated photocurrent responses of 528 (1) and 357 uA/cm2 (2). Density function theory (DFT) calculation on the frontier orbitals of 1 and 2 were useful in understanding these differences in catalytic performance.

In Situ Generation of Bifunctional Fe-Doped MoS2 Nanocanopies for Efficient Electrocatalytic Water Splitting.

Design and synthesis of non-noble metal electrocatalysts with high activity and durability for the electrolysis of water is of great significance for energy conversion and storage. In this work, we prepared a series of Fe-doped MoS2 nanomaterials by simple one-pot solvothermal reactions of (NH4)2MoS4 with FeCl3·6H2O. An optimized working electrode of Fe-MoS2-5 displayed high hydrogen evolution reaction (HER) activity with a relatively small overpotential of 173 mV to achieve a current density of 10 mA cm-2 in 0.5 M H2SO4, along with no significant change in catalytic performance even after 1000 cyclic voltammetry (CV) cycles. Fe-MoS2 nanoparticles on nickel foam (NF; denoted as Fe-MoS2/NF) exhibited an overpotential of 230 mV at 20 mA cm-2 for the oxygen evolution reaction (OER) and 153 mV at 10 mA cm-2 for the HER in 1.0 M KOH electrolyte. Fe-MoS2/NF was stable for more than 140 h under these conditions. Furthermore, the two electrode system of Fe-MoS2/NF (anode)//Fe-MoS2/NF (cathode) electrodes demonstrated excellent electrocatalytic activity toward overall water splitting with a low potential of 1.52 V at 10 mA cm-2 in 1.0 M KOH electrolyte.

Large-Scale, Bottom-Up Synthesis of Binary Metal-Organic Framework Nanosheets for Efficient Water Oxidation.

Ultrathin metal-organic framework (MOF) nanosheets (NSs) offer potential for many applications, but the synthetic strategies are largely limited to top-down, low-yield exfoliation methods. Herein, Ni-M-MOF (M=Fe, Al, Co, Mn, Zn, and Cd) NSs are reported with a thickness of only several atomic layers, prepared by a large-scale, bottom-up solvothermal method. The solvent mixture of N,N-dimethylacetamide and water plays key role in controlling the formation of these two-dimensional MOF NSs. The MOF NSs can be directly used as efficient electrocatalysts for the oxygen evolution reaction, in which the Ni-Fe-MOF NSs deliver a current density of 10 mA cm-2 at a low overpotential of 221 mV with a small Tafel slope of 56.0 mV dec-1 , and exhibit excellent stability for at least 20 h without obvious activity decay. Density functional theory calculations on the energy barriers for OER occurring at different metal sites confirm that Fe is the active site for OER at Ni-Fe-MOF NSs.

Switchable Chemoselective Transfer Hydrogenations of Unsaturated Carbonyls Using Copper(I) N-Donor Thiolate Clusters.

Unsaturated alcohols and saturated carbonyls are important chemical, pharmaceutical, and biochemical intermediates. We herein report an efficient transfer hydrogenation protocol in which conversion of unsaturated carbonyl compounds to either unsaturated alcohols or saturated carbonyls was catalyzed by Cu(I) N-donor thiolate clusters along with changing hydrogen source (isopropanol or butanol) and base (NaOH or K2CO3). Mechanistic studies supported by DFT transition state modeling indicate that such a chemoselectivity can be explained by the relative concentrations of Cu(I) monohydride and protonated Cu(I) hydride complexes in each catalytic system.

Post-synthetic Modification of a Two-Dimensional Metal-Organic Framework via Photodimerization Enables Highly Selective Luminescent Sensing of Aluminum(III).

Reaction of Cd(NO3)2·4H2O with 5-fluoro-1,3-bis[2-(4-pyridyl)ethenyl]benzene (5-F-1,3-bpeb) and 1,3-benzenedicarboxylic acid (1,3-H2BDC) under the solvothermal conditions gave rise to a two-dimensional metal-organic framework (MOF) [{Cd2(5-F-1,3-bpeb)2(1,3-BDC)2}·0.5DMF·2H2O] n (1). Compound 1 was postmodified by a photodimerization reaction between 5-F-1,3-bpeb ligands to yield [{Cd2( syn-dftpmcp)(1,3-BDC)2}·0.5DMF·H2O] n ( syn-dftpmcp = syn-3,4,12,13-tetrakis(4-pyridyl)-8,17-bisfluoro-1,2,9,10-diethano[2.2]metacyclophane) (2). Compounds 1 and 2 have 2D networks built from linking one-dimensional [Cd2(1,3-BDC)2] n chains via 5-F-1,3-bpeb or syn-dftpmcp bridges. After such a post-synthetic modification, compound 2, relative to 1, can probe Al3+ by using a luminescent quenching approach with much higher selectivity and sensitivity.

Thermogelling 3D Systems towards Stem Cell-Based Tissue Regeneration Therapies.

Stem cell culturing and differentiation is a very important research direction for tissue engineering. Thermogels are well suited for encapsulating cells because of their non-biotoxic nature and mild sol-gel transition as temperature increases. In particular, thermogels provide a 3D growth environment for stem cell growth, which is more similar to the extracellular matrix than flat substrates, so thermogels as a medium can overcome many of the cell abnormalities caused by 2D cell growth. In this review, we summarize the applications of thermogels in cell and stem cell culture in recent years. We also elaborate on the methods to induce stem cell differentiation by using thermogel-based 3D scaffolds. In particular, thermogels, encapsulating specific differentiation-inducing factor and having specific structures and moduli, can induce the differentiation into the desired tissue cells. Three dimensional thermogel scaffolds that control the growth and differentiation of cells will undoubtedly have a bright future in regenerative medicine.

Nano/Mesoporous Carbon from Rice Starch for Voltammetric Detection of Ascorbic Acid.

Rice starch (RS-)based nano/mesoporous carbon (RSNMC) was prepared via a hard-templating route using cheap rice starch as a carbon source. XRD and TEM characterization indicated the formation of organized nanoporous RSNMC. Nitrogen absorption-desorption studies revealed a high surface area of up to 488 m²âˆ™g-1, uniform pore size of 3.92 nm, and pore volume of 1.14 cm³âˆ™g-1. A RSNMC-modified glassy carbon (GC) electrode was employed for the determination of ascorbic acid (AA) and exhibited a linear response in the concentration range of 0.005-6.0 mM with a detection limit of 0.003 mM. These results demonstrate that RSNMC has potential as an advanced and cheap electrode material for electrochemical sensing and other electrocatalytic applications.

Ligand-Free RuCl3-Catalyzed Alkylation of Methylazaarenes with Alcohols.

RuCl3 efficiently catalyzes the alkylation of methylquinolines, methylpyridines, 2-methyl-benzooxazoles, and 2-methyl-quinoxalines with alkyl- or aryl-alcohols as alkylating agents. This synthetically useful and atom economical transformation does not require additional ligands. The mechanistic study indicated the alkylation reaction underwent a stepwise transfer hydrogenation, aldol condensation, and hydrogenation reaction pathway.

Luminescent Zn(II) Coordination Polymers for Highly Selective Sensing of Cr(III) and Cr(VI) in Water.

Three photoluminescent zinc coordination polymers (CPs), {[Zn2(tpeb)2(2,5-tdc)(2,5-Htdc)2]·2H2O}n (1), {[Zn2(tpeb)2(1,4-ndc)(1,4-Hndc)2]·2.6H2O}n (2), and {[Zn2(tpeb)2(2,3-ndc)2]·H2O}n (3) (tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene, 2,5-tdc = 2,5-thiophenedicarboxylic acid, 1,4-ndc = 1,4-naphthalenedicarboxylic acid, and 2,3-ndc = 2,3-naphthalenedicarboxylic acid) were prepared from reactions of Zn(NO3)2·6H2O with tpeb and 2,5-H2tdc, 1,4-H2ndc, or 2,3-H2ndc under solvothermal conditions. Compound 1 has a two-dimensional (2D) grid-like network formed from bridging 1D [Zn(tpeb)]n chains via 2,5-tdc dianions. 2 and 3 possess similar one-dimensional (1D) double-chain structures derived from bridging the [Zn(tpeb)]n chains via pairs of 1,4-ndc or 2,3-ndc ligands. The solid-state, visible emission by 1-3 was quenched by Cr3+, CrO42-, and Cr2O72- ions in water with detection limits by the most responsive complex 3 of 0.88 ppb for Cr3+ and 2.623 ppb for Cr2O72- (pH = 3) or 1.734 ppb for CrO42- (pH = 12). These values are well below the permissible limits set by the USEPA and European Union and the lowest so far reported for any bi/trifunctional CPs sensors. The mechanism of Cr3+ luminescence quenching involves irreversible coordination to free pyridyl sites in the CP framework, while the Cr6+ quenching involves reversible overlap of the absorption bands of the analytes with those of the excitation and/or emission bands for 3.

Palladium(II) Chloride Complexes of N,N'-Disubstituted Imidazole-2-thiones: Syntheses, Structures, and Catalytic Performances in Suzuki-Miyaura and Sonogashira Coupling Reactions.

Reactions of PdCl2 with 2 equiv of N,N'-disubstituted-imidazole-2-thiones R1R2C3N2S (R1 = R2 = Me (1a), iPr (1b), Cy (1c), C6Me3H2 (1d); R1 = Me, R2 = Ph (1e)) under the different conditions afford five mononuclear complexes trans-[(R1R2C3N2S)2PdCl2] (R1 = R2 = Me (2a), iPr (2b), Cy (2c), C6Me3H2 (2d); R1 = Me, R2 = Ph (2e)) and five binuclear Pd(II) complexes [(PdCl2){µ-(R1R2C3N2S)}]2 (R1 = R2 = Me (3a), iPr (3b), Cy (3c), C6Me3H2 (3d); R1 = Me, R2 = Ph (3e)), respectively. Complexes 2a-2e are easily converted into the corresponding 3a-3e by adding equimolar PdCl2 in refluxing MeOH, while the reverse reaction is achieved at room temperature by addition of 2 equiv of 1a-1e. In 2b, 2d, and 2e, each Pd(II) holds a distorted square planar geometry completed by two trans Cl atoms and two trans S atoms. Complexes 3a-3e have a dimeric [Pd2S2] structure in which two {PdCl2} units are interlinked by two N,N'-disubstituted-imidazole-2-thiones. Each Pd(II) adopts a distorted square planar geometry accomplished by two cis Cl atoms and two cis bridging S atoms. Among them, complex 3d has the two largest C6Me3H2 groups on the 2 and 5 positions of imidazole-2-thione, the longest Pd-µ-S bond, the largest S-Pd-S angle, and displays the highest catalytic activity toward Suzuki-Miyaura and copper-free Sonogashira cross-coupling reactions, which are confirmed by density functional theory calculations. The results provide an interesting insight into the introduction of various substituent groups into the periphery ligands of coordination complex-based catalysts, which could tune their geometric structures to acquire the best catalytic activity toward organic reactions.

A Cationic Coordination Polymer and Its Orange II Anion-Exchanged Products: Isolation, Structural Characterization, Photocurrent Responses, and Dielectric Properties.

Solvothermal reactions of AgNO3 with N1,N4-bis(5-fluoropyridin-3-yl)succinamide (bfps) in MeCN afforded the one-dimensional cationic coordination polymer {[Ag(bfps)]NO3}n (1). Upon treatment of 1 with the anionic azo dye orange II (NaOII) in aqueous solution, the NO3- anions of 1 could be gradually exchanged by the OII- anions via an anion-exchange process. The resulting OII anion-exchanged products {[Ag(bfps)](NO3)0.85(OII)0.15}n (2) and {[Ag(bfps)](NO3)0.1(OII)0.9}n (3) were formed by different molar ratios of 1 and the newly formed phase "{[Ag(bfps)](OII)}n" (4), confirmed by PXRD patterns. Relative to those of the precursors 1 and NaOII, complexes 2 and 3 demonstrated enlarged photocurrent responses and reduced dielectric constants and dielectric losses, which could be correlated with the OII- contents in their structures. Complex 3 acquired a stable anodic photocurrent of 12.06 µA, which was 4.9 times higher than that of 1. The dielectric constant (εr = 4.2) and dielectric loss (0.002) of 3 were nearly frequency independent in the range from 1 to 106 Hz. The results provide an interesting insight into the rational assembly of CP-dye complexes and their tunable optoelectronic applications.