Hollow POM@MOF-derived Porous NiMo6 @Co3 O4 for Biothiol Colorimetric Detection.

Developing highly active and sensitive peroxidase mimics for L -cysteine (L -Cys) colorimetric detection is very important for biotechnology and medical diagnosis. Herein, polyoxometalate-doped porous Co3 O4 composite (NiMo6 @Co3 O4 ) was designed and prepared for the first time. Compared with pure and commercial Co3 O4 , NiMo6 @Co3 O4 (n) composites exhibit the enhanced peroxidase-mimicking activities and stabilities due to the strong synergistic effect between porous Co3 O4 and multi-electron NiMo6 clusters. Moreover, the peroxidase-mimicking activities of NiMo6 @Co3 O4 (n) composites are heavily dependent on the doping mass of NiMo6 , and the optimized NiMo6 @Co3 O4 (2) exhibits the superlative peroxidase-mimicking activity. More importantly, a sensitive L -Cys colorimetric detection is developed with the sensitivity of 0.023 µM-1 and the detection limit at least 0.018 µM in the linear range of 1-20 µM, which is by far the best enzyme-mimetic performances, to the best our knowledge.

Effects of Polyoxometalates on the Hydroxylation of N-Heterocyclic Ligands.

Four polyoxometalate (POM)-based Cu complexes with the hydroxylated pyridine analogue 3-(2-hydroxylpyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl (btpo), H3{[Cu2(btpo)2](PW12O40)}·2H2O (1), H3{[Cu2(btpo)2](PMo12O40)}·2H2O (2), H2{[Cu2(btpo)2](SiW12O40)·SO4 (3), and H4{[Cu4(btpo)4](SiW12O40)}·8H2O (4), were synthesized hydrothermally under acid conditions. Single-crystal X-ray structural analysis reveals that 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl was hydroxylated into btpo in compounds 1-4, again providing structural evidence for the Gillard mechanism, in which H2O as a weak nucleophile can attack the α-C atom of N-heterocyclic molecules at a lower pH value (ca. 1.0) with the help of POMs.

Development of a Uricase-Free Colorimetric Biosensor for Uric Acid Based on PPy-Coated Polyoxometalate-Encapsulated Fourfold Helical Metal-Organic Frameworks.

Developing a new cost-effective and reliable approach used for the detection of uric acid (UA) with no requirement of uricase is still very challenging. Herein, an easily realized, cost-effective, and uricase-free approach is reported for selective colorimetric biosensing of UA utilizing polypyrrole (PPy)-coated polyoxometalate-encapsulated fourfold helical metal-organic frameworks Ag5[bimt]2[PMo12O40]·2H2O (Ag5PMo12) as a monolithic peroxidase mimic. It is demonstrated that the as-obtained Ag5PMo12@PPy possesses excellent peroxidase-like activity originated from the synergistic effect to induce catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to green oxTMB in the presence of H2O2. Then, the green oxTMB can be selectively converted to colorless TMB induced by UA; thus, UA can inhibit the catalytic oxidation of TMB. Based on these results, a uricase-free colorimetric biosensor for UA is achieved with a linear detection range of 1-50 µM and a detection limit of 0.47 µM. More importantly, the developed biosensor is suited for simple-operated and good reliable UA detection in clinical samples, showing promising application ability in clinical diagnosis and relative fields.

Heightened Integration of POM-based Metal-Organic Frameworks with Functionalized Single-Walled Carbon Nanotubes for Superior Energy Storage.

To increase the conductivity of polyoxometalate-based metal-organic frameworks (POMOFs) and promote their applications in the field of energy storage, herein, a simple approach was employed to improve their overall electrochemical performances by introducing a functionalized single-walled carbon nanotubes (SWNT-COOH). A new POMOF compound, [Cu18 (trz)12 Cl3 (H2 O)2 ][PW12 O40 ] (CuPW), was successfully synthesized, then the size-matched functionalized SWNT-COOH was introduced to fabricate CuPW/SWNT-COOH composite (PMNT-COOH) by employing a simple sonication-driven periodic functionalization strategy. When the PMNT-COOH nanocomposite was used as the anode material for Lithium-ion batteries (LIBs), PMNT-COOH(3) (CuPWNC:SWNT-COOH=3:1) showed superior behavior of energy storage, a high reversible capacity of 885 mA h g-1 up to a cycle life of 170 cycles. The electrochemical results indicate that the uniform packing of SWNT-COOH provided a favored contact between the electrolyte and the electrode, resulting in enhanced specific capacity during lithium insertion/extraction process. This fabrication of PMNT-COOH nanocomposite opens new avenues for the design and synthesis of new generation electrode materials for LIBs.

POMOF/SWNT Nanocomposites with Prominent Peroxidase-Mimicking Activity for l-Cysteine "On-Off Switch" Colorimetric Biosensing.

In order to explore novel colorimetric biosensors with high sensibility and selectivity, two new Keggin polyoxometalates (POMs)-based Cu-trz (1,2,4-triazole) metal-organic frameworks (MOFs) with suitable specific surface areas and multiple active sites were favorably fabricated; then single-walled carbon nanotubes (SWNTs) were merged with new POMOFs to construct POMOF/SWNT nanocomposites. Herein, POMOF/SWNT nanocomposites as peroxidase mimics were explored for the first time, and the peroxidase-mimicking activity of the prepared POMOF/SWNT nanocomposites is heavily dependent on the mass ratio of POMOFs and SWNTs, in which the maximum activity is achieved at the mass ratio of 2.5:1 (named PMNT-2). More importantly, PMNT-2 exhibits the lowest limit of detection (0.103 µM) among all reported materials to date and the assumable selectivity toward l-cysteine (l-Cys) detection. With these findings, a convenient, sensitive, and effective "on-off switch" colorimetric platform for l-Cys detection has been successfully developed, providing a promising prospect in the biosensors and clinical diagnosis fields.

Confined Molybdenum Phosphide in P-Doped Porous Carbon as Efficient Electrocatalysts for Hydrogen Evolution.

Highly efficient electrocatalysts for hydrogen evolution reactions (HER) are crucial for electrochemical water splitting, where high-cost and low-abundance Pt-based materials are the benchmark catalysts for HER. Herein, we report the fabrication of MoP nanoparticles confined in P-doped porous carbon (MoP@PC) via a metal-organic framework-assisted route for the first time. Remarkably, due to the synergistic effects of MoP nanocrystals, P dopant, and porous carbon, the resulting MoP@PC composite exhibits superior HER catalytic activity with an onset overpotential of 97 mV, a Tafel slope of 59.3 mV dec-1, and good long-term durability, which compares to those of most reported MoP-based HER catalysts. Most importantly, the work opens a new route in the development of high-performance nonprecious HER electrocatalysts derived from MOFs.

Fabrication and Electrochemical Performance of Polyoxometalate-Based Three-Dimensional Metal Organic Frameworks Containing Carbene Nanocages.

Two new polyoxometalate (POM)-based three-dimensional metal organic carbene frameworks, [Ag10(trz)4(H2O)2][HPW12O40] (POMs@MCNCs-1) and [Ag10(trz)4(H2O)6][H2SiW12O40] (POMs@MCNCs-2), were hydrothermally synthesized, in which Keggin-type polyoxoanions as templates induce the formation of two different kinds of metal-carbene nanocages (MCNCs) for the first time. Combination of the reversible multielectron redox behavior and electron storage functions of POMs with the good electrical conductivity of the single-walled carbon nanotubes (SWNTs) renders the POMs@MCNCs-1/SWNT composite excellent electrochemical performance and good stability as anode materials of lithium-ion batteries, with up to 2000 mA h g-1 for the first discharge capacity and ca. 859 mA h g-1 for the second cycle at a current density of 100 mA g-1. The successful fabrication of unprecedented MCNCs into the POM-based three-dimensional metal-organic frameworks in the present work must initiate extensive research interests in diverse fields.

Assembly of Multifold Helical Polyoxometalate-Based Metal-Organic Frameworks as Anode Materials in Lithium-Ion Batteries.

For exploring the multifold helical fabrication of polyoxometalate (POM)-based hybrid compounds, four POM-based crystalline compounds with different meso-helices, H3[Ag27(trz)16(H2O)6][SiW12O40]2·5H2O (1), H[Ag27(trz)16(H2O)4][PW12O40]2·2H2O (2), [Ag23(trz)14(H2O)2][HSiW12O40] (3), and [Ag23(trz)14(H2O)2][PW12O40] (4), were successfully isolated by using the delicate 1,2,3-triazole ligand and silver ions in this work. Crystal analysis reveals that compounds 1 and 2 and compounds 3 and 4 are isomorphous and display 2-/4-fold mixed meso-helices and simple 2-fold meso-helices, respectively. In addition, due to the reversible multielectron redox behavior and electron storage functions of POMs, compounds 1 and 3 were studied as anode materials in lithium-ion batteries (LIBs). Compounds 1 and 3 show very high lithiation capacities (1356 and 1140 mAh g-1, respectively) in the initial cycle, which are much higher than those of (NBu4)4[SiW12O40] and commercial graphite at the current density of 100 mA g-1. More importantly, both compounds also show good stable performance after 100 cycles.

Highly efficient hydrogen evolution electrocatalysts based on coupled molybdenum phosphide and reduced graphene oxide derived from MOFs.

A coupled hybrid of molybdenum phosphide (MoP) and reduced graphene oxide has been prepared for the first time utilizing Mo-MOFs as precursors through a facile method. The nanocomposite exhibits superior electrocatalytic performance towards the HER, and is one of the best high-performance MoP-based electrocatalysts under acidic conditions reported so far.

Controllable porosity conversion of metal-organic frameworks composed of natural ingredients for drug delivery.

Two extremely rare ß-cyclodextrin (ß-CD) supported metal-organic frameworks (MOFs), CD-MOF-1 and CD-MOF-2, were induced to crystallize for the first time through a template-induced approach. The targeted CD-MOFs were employed to perform controlled drug delivery and cytotoxicity assays that confirmed their favourable biological potential of being used as drug carriers.

Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries.

A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag5(pyttz)3·Cl·(H2O)][H3SiMo12O40]·3H2O (1), [Ag5(trz)6][H5SiMo12O40] (2), [Ag5(trz)6][H5GeMo12O40] (3), and [Ag5(trz)6][H4PW12O40] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2-4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1-4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g-1 for 1 and 1452 mAh g-1 for 2, and this stabilized at 520 mAh g-1 for 1 and 570 mAh g-1 for 2 after 100 cycles at a current density of 100 mA g-1. The performances are better than that of (NBu4)4[SiMo12O40] matrix and commercial graphite anodes.

Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger.

A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1-3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal-organic framework) with large cell volume in a range of 87968-88800 Å(3) and large pore volume of about 68%. HLJU 1-3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution.

POM species, temperature and counterions modulated the various dimensionalities of POM-based metal-organic frameworks.

To investigate the influence of POM species, temperature and counterions on the structures of POM-MOFs containing Cu-tda second building units (SBUs), six new complexes with various dimensionalities, e.g. three dimensional (3D) [Cu(H2tda)(H2O)2]4[SiW12O40]·12H2O (), two dimensional (2D) [Cu2(H2tda)2(H2O)3]·[Cu(H2tda)(H2O)2]·[PMo12O40]·5H2O (), H-bond 2D [Cu(H2tda)(H2O)2]3·[PMo12O40]·[Cu(Htda)(H2O)3]·8H2O (), one dimensional (1D) [Cu2(H2tda)2(H2O)4]2·[Cu2(tda)2(H2O)4]·[HPW12O40]·5H2O (), 1D [Cu2(H2tda)2(H2O)4][SiW12O40]·(TMA)2·3H2O (), and zero dimensional (0D) [Cu(H2tda)(H2O)3][SiW12O40]·(TMA)3·H2O (), were isolated depending on the reaction conditions. It is observed that the POM species, temperature and counterions exhibit an essential effect on the structures, which results in the formation of various dimensional POM-MOF complexes . In addition, photocatalytic degradation of RhB by complexes , and under UV irradiation was also investigated.

Structure refinement and photocatalytic properties of porous POMCPs by selecting the isomerous PYTTZ.

Two polyoxometalate-based coordination polymers (POMCPs) constructed form Keggin POMs and Ag(+) with pyttz were synthesized: [Ag4(H2pyttz-I)(H2pyttz-II)(Hpyttz-II)][HSiW12O40]·4H2O (1) and [Ag4(H2pyttz-II)(Hpyttz-II)2][H2SiW12O40]·3H2O (2) (H2pyttz-I = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl; H2pyttz-II = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl). Both compounds have similar building units, similar stick-like units and similar 1D inorganic chains, but finally form the different motifs of tunnels (tunnel A in 1 and tunnel A&B in 2). By careful inspection of the structures of 1 and 2, it is believed that the isomerous pyttz molecules can precisely refine the structure of porous POMCPs without changing the underlying framework, which favors the study of the structure-activity relationship of POMCPs. Furthermore, the results of the photocatalytic activities show that compound 2 exhibits higher photocatalytic activity than that of compound 1, which is consistent with their structural characterization.

An organic-inorganic hybrid semiconductor material based on Lindqvist polyoxomolybdate and a tetra-nuclear copper complex containing two different ligands.

A 3D organic-inorganic hybrid compound based on the Lindqvist-type polyoxometalate, [{Cu(phen)}3{Cu(µ2-ox)3}{Mo6O19}] (1) (phen = 1,10-phenanthroline, ox = oxalate), has been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR, TG, PXRD, XPS, UV-vis, and single-crystal X-ray diffraction. In compound 1, three C2O4(2-) ligands bridge one Cu atom and three Cu(phen) fragments to form a tetra-nuclear copper(II) coordination complex [{Cu(phen)}3{Cu(µ2-ox)3}](2+) unit. The six-node [Mo6O19](2-) clusters are interweaved by the 6-connected tetranuclear copper(II) complex units into an intricate 3D network structure, exhibiting a 4(12)·6(3)-nbo (sodium chloride-type) topology. Compound 1 exhibits the highest connectivity of Lindqvist-type POM hybrid materials. The electrochemical behavior of 1-CPE has been investigated in detail. Furthermore, a diffuse reflectivity spectrum of 1 reveals the presence of an optical band gap and the nature of semiconductivity with a large energy gap. A magnetic susceptibility study reveals predominant antiferromagnetic interactions between the Cu(II) bridge units.

An unprecedented 3D POM-Ag architecture with intertwined and homological helical structures.

A new hybrid compound, Na[Ag6(pyttz)2(H2O)][PMo12O40] (pyttz = 3-(pyrid-3-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), has been hydrothermally synthesized and structurally characterized by routine techniques. X-ray diffraction analysis reveals that the title compound is constructed by the 2D Ag-pyttz coordination polymer and 3D Ag-POM architecture with helix. A fascinating structural feature is the assembling fashion of the right- and left-helical chain, namely, the helical chains with different orientations are intertwined with each other forming intertwined double helical layers along the c-axis, and the identical left- or right-handed helical chains are fused together in a hand-by-hand mode generating another homological helical layer along the a-axis. As a result, these helical layers intersect each other obtaining an unprecedented 3D POM-Ag inorganic architecture. Note that the 3D framework with a helix constructed by POMs and metal ions has never been observed up to date. Additionally, its photocatalytic degradation of RhB was also investigated.

Secondary spacer modulated assembly of polyoxometalate based metal-organic frameworks.

To investigate the influence of a secondary spacer on the resulting structures of POMOFs containing pytz, five new compounds with different dimensionalities, [Cu(5)(2-pytz)(6)(H(2)O)(4)][SiMo(12)O(40)]·3H(2)O (1), [Cu(3)(2-pytz)(4)bipy][H(2)SiMo(12)O(40)]·bipy (2), [Cu(3)(2-pytz)(2)(bipy)(4)(H(2)O)(6)][H(4)SiW(12)O(40)](2)·6H(2)O (3), [Cu(2)(2-pytz)(phen)(OH)](2)[SiW(12)O(40)]·H(2)O (4), [Cu(3)(4-pytz)(4)(H(2)O)(4)][H(2)SiW(12)O(40)]·2H(2)O (5), were synthesized. When only 2-pytz was employed, compound 1 with a 3D framework was obtained, whereas when the secondary spacers (4,4'-bipy, phen and 4-pytz) were introduced into the reaction system of 1, compounds 2-5 were obtained and exhibit a broad range of structures, including 0D, 1D, 2D and 3D frameworks. It can be observed from the architectures of compounds 1-5 that the secondary spacers have a great effect on the structures of the MOFs, which results in the formation of various dimensional POMOF compounds. Additionally, photocatalytic experiments of 1-5 for the photocatalytic degradation of RhB under UV irradiation were also investigated.

catena-Poly[[(5-carb-oxy-2H-1,2,3-triazole-4-carboxyl-ato-κN,O)sodium]-di-µ-aqua-κO:O].

In the title coordination polymer, [Na(C(4)H(2)N(3)O(4))(H(2)O)(2)](n), the Na(I) atom is six-coordinated by one O atom and one N atom from a 2H-1,2,3-triazole-4-carb-oxy-5-carboxyl-ate ligand and four O atoms from four water mol-ecules, forming a distorted octa-hedal geometry. The Na(I) atoms are bridged by water mol-ecules into a chain structure along [100]. Inter-molecular N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds connect the chains. An intra-molecular O-H⋯O hydrogen bond between the carboxyl-ate groups is observed.

Assemblies of copper bis(triazole) coordination polymers using the same keggin polyoxometalate template.

Four inorganic-organic hybrid compounds, [Cu(I)(4)(bte)(4)(SiW(12)O(40))] (1), [Cu(II)(2)(bte)(4)(SiW(12)O(40))].4H(2)O (2) [bte = 1,2-bis(1,2,4-triazol-1-yl)ethane], [Cu(I)(4)(btb)(2)(SiW(12)O(40))].2H(2)O (3), and [Cu(II)(2)(btb)(4)(SiW(12)O(40))].2H(2)O (4) [btb = 1,4-bis(1,2,4-triazol-1-yl)butane], were hydrothermally synthesized through use of the same Keggin polyoxometalate as the template and tuning the molar ratio of the bis(triazole) ligand to the Cu(II) ion. The ratio of the bis(triazole) ligand to Cu(II) has a crucial influence on the structures of this series. Single-crystal X-ray diffraction analyses indicate that compound 1 is constructed by tetranuclear ring-connecting chains and polymerized [Cu(bte)](+) chains, between which SiW(12) anions are inserted to form a three-dimensional (3D) structure. Compound 2 shows a (4(4).6(2)) two-dimensional grid sheet. The discrete SiW(12) anions are sandwiched by the sheets, just like "hamburgers". Compound 3 presents channel-like [Cu(2)(btb)](2+) polymerized chains, which are further connected by SiW(12) anions to construct a 3D framework. Compound 4 exhibits a (6(6)) 3D Cu-btb framework with hexagonal channels, into which the tetradentate SiW(12) anions are incorporated. The thermal stabilities of the compounds are discussed.

Assembly of the highest connectivity Wells-Dawson polyoxometalate coordination polymer: the use of organic ligand flexibility.

Through tuning the length of flexible bis(triazole) ligands and different metal ion coordination geometries, four Wells-Dawson polyoxoanion-based hybrid compounds, [Cu 6(btp) 3(P 2W 18O 62)].3H 2O ( 1) (btp = 1,3-bis(1,2,4-triazol-1-y1)propane), [Cu 6(btb) 3((P 2W 18O 62)].2H 2O ( 2), [Cu 3(btb) 6(P 2W 18O 62)].6H 2O (btb = 1,4-bis(1,2,4-triazol-1-y1)butane) ( 3), and [Cu 3(btx) 5.5((P 2W 18O 62)].4H 2O (btx = 1,6-bis(1,2,4-triazol-1-y1)hexane) ( 4), were synthesized and structurally characterized. In compound 1, the metal-organic motif exhibits a ladder-like chain, which is further fused by the ennead-dentate [P 2W 18O 62] (6-) anions to construct a 3D structure. In compound 2, the metal-organic motif exhibits an interesting Cu-btb grid layer, and the ennead-dentate polyoxoanions are sandwiched by two Cu-btb layers to construct a 3D structure. Compound 3 exhibits a (4 (2).6 (2).8 (2)) 3D Cu-btb framework with square and hexagonal channels arranged alternately. The hexa-dentate polyoxoanions incorporate only into the hexagonal channels. In compound 4, there exist two sets of (6 (1).10 (2)) 2(6 (1).8 (2).10 (3)) 3D Cu-btx frameworks to generate a 2-fold interpenetrated structure into which the penta-dentate polyoxoanions are inserted to construct a 3D structure. The structural analyses reveal that the length of flexible bis(triazole) ligands and metal ion coordination geometries have a synergic influence on the structures of this series. To our knowledge, they have the highest connectivity for the Wells-Dawson polyoxometalate coordination polymers to date.