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Although many satisfactory studies have been developed for biomolecule detection, the complexity of biofluids still poses a major challenge to improve the performance of nanomaterials as electrochemical sensors. Herein, unprecedented polyoxometalate-based metal-organic frameworks (POMOFs) with 8-fold meso-helical feature, [Ag5(trz)4]2[PMo12O40] (PAZ), were synthesized and explored as electrochemical sensors to detect dopamine (DA). To improve the conductivity of PAZ and the binding ability with single-walled carbon nanotubes (SWCNTs), the nanocomposite of carboxyl functionalized SWCNTs (SWCNTs-COOH) with nano-PAZ (NPAZ), NPAZ@SWCNTs-COOH, was fabricated, and transmission electron microscopy (TEM) shows that NPAZ can interact stably and uniformly with SWCNTs-COOH, owing to more defect sites on the surface of SWCNTs-COOH. The electrochemical result of NPAZ@SWCNTs-COOH/GCE towards detecting DA shows that the linear range was from 0.05 to 100 μM with a detection limit (LOD) of 8.6 nM (S/N = 3).

Anderson-type polyoxometalate containing Fe3+ and Mo6+, (NH4)3[H6Fe(III)Mo6O24] (FeMo6), was found to work as an oxidase-mimicking nanoenzyme for the first time, exhibiting the ability of catalytic oxidation of o-phenylenediamine (OPD), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTs), and 3,3′,5,5′-tetramethylbenzidine (TMB), which features easy synthesis, low cost, simple operation, and low consumption. Attributed to the nature of FeMo6 and Fenton-like effect, a novel sensor based on two consecutive “turn on” fluorescence was developed for detecting dopamine (DA) by employing the FeMo6-OPD system, and the linear range was from 1 to 100 μM with the detection limit 0.0227 μM (3σ/s). Moreover, to increase oxidase-mimic activity of FeMo6, reduced graphene oxide (rGO) loading FeMo6 composites (FeMo6@rGO (n), n = 5%, 10%, 15%) was fabricated, and results show that oxidase-like activities of FeMo6@rGO (n) are dependent on the mass ratio of FeMo6/rGO, and FeMo6@rGO (10%) exhibits the highest oxidase-mimic activity and the fastest respond time (4 min) among all reported oxidase mimic of DA to date.

Polyoxometalate-based crystalline materials as electro-active medium have exhibited excellent performances as bio/chemical sensors, particularly when synergy is reached upon combining with conductive materials. In this study, a catenane Keggin-type phosphomolybdic acid-based Ag-triazole framework and reduced graphene oxide (PMo12[6]catenane/rGO) was synthesized and employed to fabricate a modified electrode to detect the neurotransmitter dopamine (DA). Results show that PMo12[6]catenane and rGO composite modified electrode had strong catalytic activity for oxidation of DA and exhibited wide linear detection range from 1 to 90 μM with the limit of detection (LOD) of 0.890 μM and 1–44 μM with LOD 0.065 μM (S/N = 3). No interference from uric acid (UA) and ascorbic acid (AA) demonstrates that PMo12[6]catenane and rGO composite modified electrode possesses good selectivity to DA detection. The work can promote the further development of POMOFs with different structures in sensing applications.

A new polyoxometalate (POM)-templated 3-D copper(II)-triazole framework [Cu10(trz)10(OH)6(Cl)4][H3PW12O40]·2H2O (trz = 1,2,3-triazole) has been synthesized and characterized by single crystal X-ray diffraction and other routine methods. The 3-D POM/copper(II)-triazole hybrid framework with a 1-D channel possesses a pcu topology under the template of bulk Keggin-type phosphotungstate. As a new kind of peroxidase mimetic, the new compound effectively catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. The electrostatic interactions and hydrogen bonds/π-π stacking interactions among TMB, trz, and phosphotungstate are responsible for the enhancement of peroxidase-like activity. In addition, application for colorimetric sensing of H2O2 is also explored; the new compound exhibits a wide linear range (1–80 μM), low detection limit (0.21 μM), and fast response (2 min).

Two Keggin polyoxometalate (POMs) based hybrid compounds containing helix/nanocages as peroxidase-like mimics have been synthesized and structurally characterized. Single crystal X-ray diffraction analysis reveals that compound 1 exhibits a POM-pillared framework with open nanotube channels (ca. 5.6 × 5.8 A2), in which SiW12 polyanions are sandwiched between the adjacent Cu-fkz sheets with meso-helix. And an unprecedented twisted octahedral hexamer nanocage (ca. 10 × 10 A2) is observed in compound 2. Compared with the other POMs involved peroxidase-like mimics, both compounds 1 and 2 exhibit higher peroxidase-like catalytic activities, broader applications range, faster respond time and lower detection limit, which maybe attribute to the maximized synergistic effects of SiW12 clusters, fkz molecules, metal ions and the distinct structure. Based on the facts, compounds 1 and 2 as enzyme mimics might expand their application around physiological pH conditions, and can be used as one kind of effective probe to detect H2O2 in live organism.

A new polyoxometalate based hybrid compound containing Ag-Ag chain, [Ag29(trz)18][SiWV7WVI5O40] (Ag29SiW12), was synthesized by the simple one-step hydrothermal reaction of silver nitrate, 1, 2, 3- triazole (trz), and [SiW12O40]4- polyanion. Single crystal X-ray diffraction analysis shows that the [SiW12O40]4- polyanions as coordinating guests were successfully encapsulated into the metal-organic framework host matrix. The Keggin [SiW12O40]n- polyanions as templates and trz molecules as the small and delicate ligands play the decisive factors to the formation of silver chain. In addition, to improve the photocatalytic activity of the new compound Ag29SiW12, its polypyrrole (PPy) composite (PPy@Ag29SiW12) has been prepared and exhibits excellent photocatalytic activity (93.1% for MB and 48.8% for RhB) and selectivity adsorption (16.2 mg/g for MB and 1.60 mg/g for RhB) for organic dyes under the visible light radiation.

The third-order nonlinear optical properties of a series of naphthyl, phenanthrenyl, and pyrenyl substituted porphyrins have been comparatively investigated by performing the femtosecond-pulsed Z-scan measurements. Due to the expanded π system, both pyrenly substituted porphyrin ( 1 ) and phenanthrenly substituted porphyrin ( 2 ) exhibit large two-photon absorption cross sections up to 4.26 × 10 4 GM for 1 and 1.36 × 10 4 GM for 2 at the wavelength of 800 nm. The pyrenly substituted porphyrin ( 1 ) has the most excellent two-photon absorption property because of the intramolecular energy transfer from the excited pyrene moiety to the porphyrin moiety in porphyrin 1 . The results confirm that porphyrins conjugated with external π electronic systems can lead to the significant enhancement in the two-photon absorption cross-section values. This research provides a useful guideline to the design of efficient two-photon absorbing materials.

A series of heteroleptic phthalocyaninato rare earth double-decker complexes owning large two-photon absorption cross-sections were reported. The third-order nonlinear optical properties of these heteroleptic phthalocyaninato complexes were experimentally investigated by the Z-scan technique with application of femtosecond (800 nm) pulse lasers. Due to the highly delocalized π-electron system and intense π-π interactions between the phthalocyaninato macrocycles, all complexes were revealed to exhibit large two-photon absorption cross-sections with the value up to 1.83 × 10 5 GM, which are comparable to those efficient two-photon absorbing materials. The optical limiting behavior of these complexes in chloroform was also investigated by using femtosecond laser pulses. The excellent two-photon absorption properties and optical limiting performance indicate their good application potential in optoelectronic devices.

Reaction of 5-chloro-6-hydroxynicotinic acid with Ph3SnCl and sodium ethoxide in 1:1:1 stoichiometry yielded triphenyltin compound. This compound has been characterized by single crystal X-ray diffraction, elemental analysis, IR and 1H NMR spectroscopy. In the molecular structure of the title compound, the tin atoms are five-coordinated in a distorted trigonal bipyramidal geometry. The resulting structure is 1D linear polymer through an interaction between the O atoms of phenolic hydroxide and tin atoms of an adjacent molcule. The compound exhibit high antitumor activity.

Four distannoxane dimers [ClR2SnOSnR2X]2 (X=Cl, R=PhCH2 1, 2-FC6H4CH2 2, 2-ClC6H4CH2 3, X=OH, R=2,4-ChC6H3CH2 4) have been synthesized by the hydrolytic reaction of (PhCH2)2SnCh with soditma alkoxides. And all these four complexs were characterized by elemental analysis, IR, 1H NMR spectroscopies and X-ray diffraction. All compounds were assigned tetranuclear distannoxane structures in solid state, which contain so-called ladder arrangement with a central planar Sn2O2 four-membered ring. The endo- and exo-cyclic Sn atoms are both five-coordinate, and have distorted trigonal bipyramidal geometries.

Two new polyoxometalate-templated organic–inorganic hybrid compounds with different metal–organic frameworks, [Ag5(trz)6][H4PMo12O40] (1) and [Ag10(trz)8][HPMo12O40] (2) (trz = 1,2,4-triazole), have been prepared based on the same organic ligands under different pH values. Compound 1 exhibits a honeycomb 2D [Ag5(trz)6] network and 3D graphite-like hybrid framework, and compound 2 exhibits a 3D {Ag3[Ag6(trz)6][Ag(trz)2]} framework with 2D channels, in which [PMo12O40]3− polyanions locate in the center of channels. To the best of our knowledge, [PMo12O40]3− polyanions represent the highest coordination number in 1 and terminal oxygen coordination number in 2 of Keggin POMs up to date. A comparison of two compounds demonstrates that the coordination mode of 1,2,4-triazole ligands and Keggin POMs templates have important influences on the assembly of different frameworks. In addition, compounds 1 and 2 exhibit good photocatalytic degradation of Rhodamine-B, and are very stable and easily recyclable as well.

A novel α-cyclodextrin based metal–organic framework (CD-MOF) with chiral helices, K3(C36H60O30)2·7H2O (1), was synthesized by vapor diffusion method, which contains infinitely long left-handed helical chains, interdigitated with six circumambient helical chains. Compound 1 exhibits efficient drug loading capacity and excellent sustained release behavior. In addition, by changing the synthetic method, another compound based on α-cyclodextrin, (C36H60O30)·H2O (2), was isolated by solvothermal synthesis, which contains left-handed chiral helical double channels, linked with adjacent four same helical channels. Moreover, the lower cytotoxicity of the two compounds indicates that they are a type of renewable, environmentally friendly and biocompatible drug carrier material.

By introducing isomeric organic ligands into polyoxometalate (POM) systems, two new POM-based hybrid compounds, [Cu6(m-pyttz)2(H2O)][HPMo12O40] (1) and [Ag3(p-H2pyttz)(p-Hpyttz)Cl][H2PMo12O40]·6H2O (2) (m-/p-H2pyttz = 3-(pyrid-3/4-yl)-5(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), have been hydrothermally synthesized and characterized. Single-crystal structural analysis shows the m-pyttz ligands link CuI ions to generate a two-dimensional layer with hanger-like rhombus, which is pillared by the PMo12 anions in 1. Compound 2 exhibits a three-dimensional supramolecular framework, in which PMo12 anions are building blocks facilitating the extension of the whole structure. The influence of the coordination modes of m-/p-H2pyttz on the structures is discussed in detail. Furthermore, electrochemical properties of 1 and 2 have been studied and they display excellent electrocatalytic activities toward the reduction of nitrite and hydrogen peroxide and pH-dependent electrochemical behaviors.

To rich the coordination polymer and polyoxometalate (POM) chemistry, two new hybrid compounds based on Keggin POMs with antifungal medicine fluconazole (Hfkz = [1-(2,4-difluorophenyl)-1,1-bis [(1H-1,2,4-triazol-1-yl)-methyl]methanol]), [Ag4(Hfkz)2][PW12O40] (AgFkzPW12) and [Ag4(Hfkz)2][SiW12O40] (AgFkzSiW12), have been successfully synthesized and structurally characterized. Moreover, to improve the photogenerated electron-hole pair separation properties, the surface of hybrid compounds was loaded by polypyrrole (PPy) through a chemical oxidation polymerization process in situ fabricating hybrid nanocomposites AgFkzPW12@PPy and AgFkzSiW12@PPy. As a result, the Hfkz molecules were successfully grafted onto the surface of the Keggin polyoxoanions, and their nanocomposites exhibit better photocatalytic activity than the respective matrix compounds under the irradiation of visible light.

A polyoxometalate-templated metallacycle compound, [Ag6trz6][H3PMo12O40]2·6H2O (trz = 1,2,3-triazole), has been isolated and structurally characterized. The compound represents the first example of a trigonal antiprism based metal-organic framework (MOFs) with complicated Zr6Br12 type topology, in which the trigonal antiprisms as building blocks are constructed by the Ag6trz6 space polygons and the bifunctional POMs (both as template and building block). In addition, to improve the photocatalytic activity of polyoxometalate-templated metallacycle compound, polypyrrole was loaded on its surface through a chemical oxidation polymerization process in situ. Finally, the photocatalytic activity of [Ag6trz6][H3PMo12O40]2 and PPy@[Ag6trz6][H3PMo12O40]2 under visible light was explored, and the results demonstrate that the PPy loading on the surface of POMs-based hybrid compound is feasible to improve their photocatalytic performance.

A new organic-inorganic hybrid compound based on Keggin tungstocobaltate units supported by copper complexes, [Cu(I)(2,2’-bipy)2]{[Cu(II)(2,2’-bipy)2]2[HCoW12O40]} ・ 4H2O (bipy = bipyridine), has been synthesized under hydrothermal conditions and characterized by elemental, IR, TG, and XPS analyses and X-ray single-crystal structure determination. The crystal structure is built up from bi-supported Keggin tungstocobaltate polyoxoanions {[Cu(II)(2,2’-bipy)2]2[HCoW12O40]}−, [Cu(I)(2,2’-bipy)2]+ cations and water molecules. The title compound possesses a 1D tangled helical structure composed of {[Cu(II)(2,2’-bipy)2]2[HCoW12O40]}− polyoxoanions via π・ ・ ・π interactions along the c axis. The electrochemical behavior of the title compound was studied.

Three kinds of rare earth ternary complexes of Eu 3+ with HTTA and M (M = 5-NO 2 Phen, 2,2′-Dipy and TPPO) have been synthesized and characterized using various spectral techniques such as elemental analysis, TGA-DTA, IR, UV and fluorescent. Results show that the complexes of Eu(III) emit strong red luminescence when excited by UV light. The complex Eu(TTA) 3 5NO 2 Phen posses the highest sensitized luminescent efficiency and the longest lifetime in the studied complexes. TG curves indicate that Eu(TTA) 3 5NO 2 Phen is most stable. In device ITO/PVK/Eu(TTA) 3 5NO 2 Phen/Al, Eu 3+ may be excited by intramolecular energy transfer from ligands as observed by electroluminescence. The main emitting peak at 614 nm can be attributed to the transition of 5 D 0 → 7 F 2 of Eu 3+ ion, and this process results in the enhancement of red emission from electroluminescence device.

A novel supramolecular compound based on the Keggin polyoxometalate (Hpipz)3[PMo12O40](1) (pipz = piperazine) has been synthesized and characterized. X-Ray diffraction analysis reveals that the Keggin polyanion uses all of its surface oxygen atoms (36) to attract eighteen pipz units at its periphery. This represents the highest connectivity of a Keggin polyoxoanion. The electrochemical behavior of a CPE modified with 1 (1-CPE) has been studied.

A new compound based on polyoxometalates, [Cu(bbi)]{sub 5}H[H{sub 2}W{sub 12}O{sub 40}] (1) (bbi=1,1'-(1,4-butanediyl)bis(imidazole)), has been hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and single X-ray diffraction. Compound 1 shows a twofold 3D+3D topology, and it represents the first interpenetrating network based on the isopolytungstate. The electrochemical property of compound 1 modified carbon paste electrode (1-CPE) was investigated in 1 M H{sub 2}SO{sub 4} solution, and the results indicate that 1-CPE exhibits the electrocatalytic activity toward the reduction of bromate and nitrite. Further, the non-isothermal kinetics of the thermal decomposition of compound 1 provides the dynamic parameters E (activation energy) and A (pre-exponential factor) for the pyrolytic reaction of the organic ligands. - Graphical Abstract: The 3D+3D structure representation of the first example of interpenetrating framework based on the isopolytungstate.

A polyoxometalate-based, inorganic–organic hybrid compound containing a helical structure along the a axis, [Ag(pyttz)2][H2PW12O40]·2H2O (p-pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), has been isolated and structurally characterized. Single-crystal X-ray diffraction analysis reveals that the new compound possesses two helical channels constructed by the left- and right-handed helical chains, respectively, which are fused together through sharing POMs dimer fabricating a 3-D framework with {44·53·63} {44·53·63} topolopy. The new compound displays good acid-catalytic activity toward the synthesis of Aspirin and good oxidation-catalytic activity to the decomposition of Rhodamine B dye; the catalytic reaction kinetics are discussed.