Tailoring the Coordination Microenvironment of Polymolybdate within a Metal-Organic Coordination System for Enhanced Capacitive Activity.

The design of a low-cost and efficient electrode material is crucial for electrochemical energy storage. Effectual utilization of polymolybdate as an electrode material for a supercapacitor is promising. Meanwhile, the coordination microenvironments of polymolybdate sho potential effects on its performance. Herein, we designed and synthesized four polymolybdate-based metal-organic complexes using a structure design strategy. Their structures were characterized and analyzed using single crystallographic data. The theoretical calculations revealed that the coordination microenvironments of polymolybdate play a vital role in the hydrogen ions migration. High H adsorption capacity can obviously boost the electrochemical activity. The 1-based glassy carbon electrode showed the highest specific capacitance value of 1739.4 F·g-1 at the current density of 1 A·g-1. Meanwhile, the carbon cloth-based electrode fabricated by complex 1 (1/CC) also displayed a high capacitance performance. A hybrid supercapacitor was assembled using the 1/CC electrodes and showed a high energy density of 29.0 Wh kg-1 at the power density of 0.80 kW kg-1.

Two {CuI[P4Mo6]2}-Based Coordination Polymers Incorporating In Situ Converted Tetrapyridyl Ligands for Trace Analysis of Nitrofuran Antibiotics.

Nitrofurans are important synthetic broad-spectrum antibacterial drugs with the basic structure of 5-nitrofuran. Due to their toxicity, it is essential to develop a sensitive sensor with strong anti-interference capabilities for their detection. In this work, two {P4Mo6O31}12--based compounds, [H4(HPTTP)]2{CuI[Mo12O24(OH)6(PO4)3(HPO4)(H2PO4)4]}·xH2O (x = 13 for (1), 7 for (2); HPTTP = 4,4',4″,4‴-(1H-pyrrole-2,3,4,5-tetrayl)tetrapyridine), exhibiting similar coordination but distinct stacking modes. Both compounds were synthesized and used for the electrochemical detection of nitrofuran antibiotics. The tetrapyridine-based ligand was generated in situ during assembly, and its potential mechanism was discussed. Composite electrode materials, formed by mixing graphite powder with compounds 1-2 and physically grinding them, proved to be highly effective in the electrochemical trace detection of furazolidone (FZD) and furaltadone hydrochloride (FTD·HCl) under optimal conditions. Besides, the possible electrochemical detection mechanisms of two nitro-antibiotics were studied.

"Tree"-like Multidentate Ligand-Assisted Synthesis of Polymolybdate-Based Architectures with Multinuclear Metal Clusters: Supercapacitor and Electrochemical Sensing Performances.

In this work, aiming for constructing multinuclear metal cluster-modified polymolybdate-based architectures with novel conformation, the "tree"-like multidentate ligand 5-(3-pyridyl)-1H-tetrazole) (3-ptzH) is introduced into the polymolybdate reaction system. Three new polymolybdate-based architectures with various multinuclear metal clusters, H4[Cu6(µ3-OH)2(3-ptz)6(γ-Mo8O28) (H2O)2]·2H2O (BOHU-1), H2[Ag4(3-ptz)2(Mo8O26)] (BOHU-2), and H4[Cu5(3-ptzH)2(3-ptz)2(MnMo9O32)2(H2O)4] (BOHU-3) (BOHU = Bohai University), have been prepared via the hydrothermal method and structurally characterized. In BOHU-1, a kind of pentanuclear copper cluster unit: [Cu5(µ3-OH)2(3-ptz)6]2+ is formed, which connects to construct a one-dimensional (1D) cluster-based chain. The 1D chains are extended to a two-dimensional (2D) layer via the Cu ions, which are further linked by the 4-connected [γ-Mo8O28]8- anions to build a three-dimensional (3D) framework. In BOHU-2, when a AgI ion was used as the central metal, the 3-ptz adopts different coordination modes to link the Ag ions, forming hexanuclear [Ag6(3-ptz)4]2+ cluster and finally 1D chains. These 1D cluster-based chains are connected by the 6-connected [γ-Mo8O26]4- anions to establish a 2D layer, which is further extended by [Mo8O26]n4n- 1D chains to a 3D framework. For BOHU-3, the chiral [MnMo9O32]6- anions are introduced and coordinated with the Cu ions to build left- and right-handed 1D chains, which are connected via the [Cu3(3-ptz)4]2+ cluster to form a 1D ladder-like chain. The effects of 3-ptz on the formation of multinuclear clusters, as well as the metals and polymolybdates on the multinuclear clusters and final structures of BOHU-1∼3, are discussed. The electrochemical performances of BOHU-1∼3 as electrode materials for supercapacitors and electrochemical sensors are investigated.

Improved capacitive performances and electrocatalytic reduction activity by regulating the bonding interaction between Zn-bistriazole-pyrazine/pyridine units and diverse Anderson-type polyoxometalates.

Electrochemical performances can be effectively improved by introducing metal-organic units (MOUs) into polyoxometalates (POMs). However, regulating the bonding strength between POMs and MOUs at the molecular level to improve the electrochemical performance is a challenging task. Three new POM-based metal-organic complexes (MOCs), namely H{Zn2(Hpytty)2(H2O)8[CrMo6(OH)6O18]}·2H2O (1), H{Zn2(Hpyttz)2(H2O)6[CrMo6(OH)6O18]}·8H2O (2), and {(µ2-OH)2Zn6(pyttz)2(H2O)10[TeMo6O24]}·2H2O (3) (H2pytty = 3-(pyrazin-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H2pyttz = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), were obtained. Single-crystal X-ray diffraction shows that the bonding strength (from the hydrogen bond to the coordination bond) between Zn-bistriazole-pyrazine/pyridine units and diverse Anderson-type POMs gradually increases from complexes 1 to 3. Glassy carbon electrodes modified with complex 3 (3-GCE) has the highest specific capacitance, which is 930 F g-1 at 1 A g-1. Moreover, carbon paste electrodes (1-3-CPEs) modified with complexes 1-3 are used as electrochemical sensors for detecting Cr(VI) ions, with limits of detection well below the World Health Organization (WHO) maximum level in drinking water.

Two new polyoxometalate-based metal-organic complexes for the detection of trace Cr(VI) and their capacitor performance.

Two new Keggin-type polyoxometalate (POM)-based metal-organic complexes (MOCs) H3[Cu2(4-dpye)2(PMo12O40)] (1) and H[Cu2(4-Hdpye)2(PMo12O40)(H2O)4]·2H2O (2) were constructed with a new N,N'-bis (4-pyrimidinecarboxamido)-1,2-ethane (4-H2dpye) ligand by the hydrothermal/solvothermal method. Complex 1 was a 2D layered structure constructed from 1D metal-organic chains [Cu(4-dpye)]n and Keggin-type [PMo12O40]3- polyoxoanions. Complex 2 displays a 3D supramolecular framework formed by discrete [PMo12O40]3- polyoxoanions and binuclear metal-organic loops [Cu2(4-Hdpye)2]. The electrocatalytic behaviors of carbon paste electrodes modified by complexes 1 and 2 (1-CPE and 2-CPE) were investigated. The 1-CPE and 2-CPE were used as electrochemical sensors to detect trace Cr(vi), and the low limits of detection (LOD) are 1.27 × 10-7 M for 1 and 1.71 × 10-7 M for 2, which are lower than the maximum allowable concentration of Cr(vi) in drinking water specified by the World Health Organization (WHO). In addition, the performances of complexes 1 and 2 modified carbon cloth electrodes (1-CC and 2-CC) as supercapacitor materials have also been studied. The influence of the structure on electrocatalytic and capacitor performances is discussed.

Immobilization of phosphotungstate through doping in polypyrrole for supercapacitors.

Immobilization of phosphotungstate is achieved through doping in polypyrrole via the electrochemical deposition of polypyrrole (PPy) in the presence of the phosphotungstate anions (PW12) on carbon nanotube film. Electrochemical stability in neutral solution is realized for PW12 in the prepared ECNT-PPy/5PW12, owing to the proton sponge provided by PPy. ECNT-PPy/5PW12 shows a high areal capacitance of 1300.0 mF cm-2 in LiCl solution at 1 mA cm-2. ECNT-PPy/5PW12 also displays high rate capability and good cyclic stability due to the interaction of incorporated PW12 and the polymer matrix. ECNT-PPy/5PW12 can retain 78.6% and 92.0% of its capacitance with 40-fold current increase and after 10 000 galvanostatic charge/discharge cycles, respectively. An asymmetric supercapacitor with the ECNT-PPy/5PW12 anode and CNT-MnO2 cathode demonstrates high volumetric energy density (4.71 mW h cm-3 at 13.85 mW cm-3) and long cycle life (90.0% capacitance retention after 10 000 charge/discharge cycles).

A series of Anderson-type polyoxometalate-based metal-organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts.

Seven polyoxometalate-based (POM) metal-organic complexes (MOCs) with different pyridyl-amide ligands were hydrothermally synthesized and structurally characterized. In 1, the [CrMo6(OH)5O19](4-) (CrMo6) polyoxoanions bridge the Cu(II) ions to generate a 1D Cu-CrMo6 inorganic double chain, which is further consolidated by the µ2-bridging 2-pdya ligands. Complex 2 exhibits a 2D layer based on [γ-Mo8O26]n(4n-) chains. In complex 3, the ß-Mo8O26 anions link the metal-organic units [Cu(4-Hdpyp)2](4+) to construct a 1D fishbone-like chain. Complex 4 shows a 3D (6,6)-connected framework constructed by the 2D inorganic network [Cu4(µ3-OH)2(H2O)4(γ-Mo8O27)] and 3-dpyh bridging ligands. In 2-4, all the [CoMo6(OH)6O18](3-) (CoMo6) anions were in situ transformed to Mo8O26(4-) or Mo8O27(6-) anions. Complexes 5 and 7 are isostructural, each [TeMo6O24](6-) (TeMo6) polyoxoanion coordinates to two Cu(II) ions to generate a discrete copper complex [Cu2(4-Hdpye)2(TeMo6O24)(H2O)6] and [Cu2(4-Hdpyb)2(TeMo6O24)(H2O)6], respectively. In complex 6, the TeMo6 polyoxoanions bridge the Cu(II) ions to generate a 2D [Cu3(TeMo6)]n inorganic layer, which is further linked by the µ2-bridging 3-dpyb ligands to form a 3D metal-organic framework. The effects of POM types and their various coordination modes, as well as the pyridyl-amide ligands on the structures of the title complexes have been discussed. Their electrochemical behavior reveals characteristic multi-electron redox processes related to Mo(VI) centers. The electrocatalytic reduction performance toward hydrogen peroxide and bromate was fully measured and discussed; both complexes exhibit excellent electrocatalytic activity towards the reduction of bromate and hydrogen peroxide. In addition, the redox potentials of complexes 5-7 are highly pH sensitive and may be used as a kind of potential pH sensor. The photocatalytic activities of the title complexes are also investigated in detail.

Novel Anderson-type [TeMo6O24](6-)-based metal-organic complexes tuned by different species and their coordination modes: assembly, various architectures and properties.

Four novel Anderson-type polyoxometalates (POMs) [TeMo6O24](6-) (TeMo6)-based metal-organic complexes (MOCs), namely, H2[Zn4(3-Hdpyp)2(TeMo6O24)2(H2O)16]·6H2O (1), [Zn3(3-dpyb)2(TeMo6O24)(H2O)12]·8H2O (2), [Cu2(4-Hdpyp)2(TeMo6O24)(H2O)6]·4H2O (3), and [Cu3(3-dpyp)2(TeMo6O24)(H2O)8]·4H2O (4) (3-dpyp = N,N'-bis(3-pyridinecarboxamide)-1,3-propane, 3-dpyb = N,N'-bis(3-pyridinecarboxamide)-1,4-butane, 4-dpyp = N,N'-bis(4-pyridinecarboxamide)-1,3-propane), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1, two TeMo6 polyoxoanions bridge Zn(II) ions to generate a discrete tetranuclear zinc complex H2[Zn4(3-Hdpyp)2(TeMo6O24)2(H2O)16]. In 2, the TeMo6 anions connect the metal-organic units [Zn3(3-dpyb)2](6+) to form an Anderson-type TeMo6-based wave-like metal-organic chain. Both the discrete tetranuclear subunits in 1 and 1D wavy chains in 2 were further extended to 2D supramolecular networks through the hydrogen bonding interactions. In complex 3, the TeMo6 anions link the metal-organic units [Cu2(4-Hdpyp)2](6+) to construct a 2D layer, which is further extended to a 3D supramolecular framework by the hydrogen bonding interactions. In complex 4, the TeMo6 polyoxoanions bridge the Cu(II) ions to generate a 2D Cu-TeMo6 inorganic layer, which is further linked by the µ2-bridging 3-dpyp ligands to form a 3D metal-organic framework. The effects of various coordination modes of TeMo6 polyanions and the bis-pyridyl-bis-amide ligands, as well as the central metals on the structures of the title complexes have been discussed. Besides, the fluorescence, electrochemical properties and photocatalytic activities of the title complexes have been investigated in detail.

Assembly and photocatalysis of two novel 3D Anderson-type polyoxometalate-based metal-organic frameworks constructed from isomeric bis(pyridylformyl)piperazine ligands.

Two novel Anderson-type polyoxometalates (POMs)-based metal-organic frameworks (MOFs), namely, H{Cu2(µ2-OH)2L(1)[CrMo6(OH)6O18]}·4H2O (), {Cu2L(2)[CrMo(VI)5Mo(V)(OH)6O18](H2O)4}·4H2O () (L(1) = N,N'-bis(3-pyridinecarboxamide)-piperazine, L(2) = N,N'-bis(4-pyridinecarboxamide)-piperazine), are hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex , the hexadentate [CrMo6(OH)6O18](3-) polyoxoanion bridges the Cu(II) ions to generate a 2D Cu-POM inorganic layer, which is further extended by the µ2-bridging L(1) ligands (via ligation of pyridyl nitrogen atoms) to form a 3D MOF with a 4,6-connected {4(4)·6(10)·8}{4(4)·6(2)} topology. Complex is also a 3D POM-based MOF exhibiting a {4(2)·8(4)} topology, which is constructed from the quadridentate [CrMo(VI)5Mo(V)(OH)6O18](4-) polyoxoanions and µ4-bridging L(2) ligands (via ligation of pyridyl nitrogen and carbonyl oxygen atoms). The different coordination modes of POM polyanions and the isomeric bis(pyridylformyl)piperazine ligands play key roles in the construction of the title complexes. In addition, the photocatalytic activities of the title complexes on the degradation of methylene blue (MB) under UV, visible light and sunlight irradiation have been investigated in detail.