A tetra Ru-substituted polyoxometalate Na10[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2] (Ru4POM) has been successfully immobilised onto glassy carbon electrodes and indium tin oxide (ITO) coated glass slides through the employment of a conducting polypyrrole matrix and the layer-by-layer (LBL) technique. The resulting Ru4POM doped polypyrrole films showed stable redox behavior associated with the Ru centres within the Ru4POM, whereas, the POM's tungsten-oxo redox centres were not accessible. The films showed pH dependent redox behavior within the pH range 2-5 whilst exhibiting excellent stability towards redox cycling. The layer-by-layer assembly was constructed onto poly(diallyldimethylammonium chloride) (PDDA) modified carbon electrodes by alternate depositions of Ru4POM and a Ru(II) metallodendrimer. The resulting Ru4POM assemblies showed stable redox behavior for the redox processes associated with Ru4POM in the pH range 2-5. The charge transfer resistance of the LBL films was calculated through AC-Impedance. Surface characterization of both the polymer and LBL Ru4POM films was carried out using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Initial investigations into the ability of the Ru4POM LBL films to electrocatalytically oxidise water at pH 7 have also been conducted.

A conducting polymer was used for the immobilization of various transition metal ion-substituted Dawson-type polyoxometalates (POMs) onto glassy carbon electrodes. Voltammetric responses of films of different thicknesses were stable within the pH domain 2-7 and reveal redox processes associated with the conducting polymer, the entrapped POMs and incorporated metal ions. The resulting POM doped 10 polypyrrole films were found to be extremely stable towards redox switching between the various redox states associated with the incorporated POM. An amperometric sensor for hydrogen peroxide detection based upon the POM doped polymer films was investigated. The detection limits were 0.3 and 0.6 uM, for the Cu 2+ -and Fe 3+ -substituted POM-doped polypyrrole films respectively, with a linear region from 0.1 up to 2mM H 2 O 2 . Surface characterization of the polymer films was carried out using atomic force 15 microscopy, x-ray photoelectron spectroscopy and scanning electron microscopy. IntroductionPolyoxometalates (POMs) are a widely increasing class of inorganic early transition metal-oxide clusters. The structural and compositional diversity among this class of compounds have 20 enabled them to be promising candidates for a wide range of applications across material science, medicine, biotechnology, nanotechnology and catalysis. [1][2][3][4][5][6][7][8][9][10][11][12] The general structure of POMs consists of MO 6 units joined together by edge or corner sharing and connected tetrahedrally to a centrally bonded heteroatom 25 (usually phosphorus or silicon). One of the MO 6 units can be removed from the structure at higher pH and substituted with different metal ions allowing for controllable molecular design.Various strategies have been used for immobilization of POMs onto different surfaces, safeguarding their inherent properties. 30 These include: sol-gel technique, 13 polyoxometalates. 38,39 Despite the high selectivity and sensitivity of enzyme-modified electrodes, 40, 41 the limitation of usage of these systems is related to the difficulty in obtaining the optimal conditions and the lack of the enzymatic activity over a period of time, 42 POMs inside the polymer matrix were accessible for voltammetric studies in acidic medium. The films exhibited stable redox responses in the pH range of 2-7. Surface characterization was carried out using the AFM, XPS and SEM. Electrocatalytic activity of the films containing iron and copper-20 substituted POMs towards the reduction of hydrogen peroxide was studied by amperometry at physiological conditions (pH 6.5) and compared with the performance of the same POMs in solution 50 and immobilized onto an electrode surface via multilayer assemblies. 19 Conducting polymer-based POM-doped 25 polypyrrole films reveal the best analytical characteristics for hydrogen peroxide reduction in comparison with some other approaches. Experimental 30 MaterialsThe potassium salts of all the substituted Dawson type polyoxometalates investigated were synthesized and characterised by both ele...

Iron-substituted crown-type polyoxometalate (POM) [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) has been successfully immobilized onto glassy carbon electrode surfaces by means of the layer-by-layer (LBL) technique employing the cationic redox active dye, methylene blue (MB). The constructed multilayers exhibit pH-dependent redox activity for both the anionic POM and the cationic dye moieties, which is in good agreement with their solution behavior. The films have been characterized by alternating current impedance, atomic force microscopy, and X-ray photoelectron spectroscopy, whereby the nature of the outer layer within the assemblies was found to have an effect upon the film's behavior. Preliminary investigations show that the POM dye-based films show electrocatalytic ability toward the reduction of hydrogen peroxide, however, only when there is an outer anionic POM layer.

No abstract

A novel bisphosphonate ligand bearing a thiophene group (AleThio) was synthesized and its covalent grafting to polyoxometalates (POMs) investigated. The hybrid polyoxomolybdate [(Mo3O8)4(O3PC(O)(C3H6NH2CH2C4H3S)PO3)4]8– [Mo12(AleThio)4] was synthesized in water by the reaction of Na2MoO4 with AleThio. It is built of four {MoVI3O8} units connected by phosphonate groups around a central Na+ ion. The reaction of the trivacant [PW9O34]9– units with CoII or NiII ions in the presence of AleThio led to the sandwich‐type anions [(PW9O34)2(OH)2(H2O)4M7(O3PC(O)(C3H6NH2CH2C4H3S)PO3)2]14– [M = Ni, Co; M7(AleThio)2]. Salts soluble in organic solvent were prepared by cation‐exchange with bis(triphenylphosphine)iminium ions. 31P NMR spectroscopy showed that Mo12(AleThio)4 is stable in acidic medium (pH ≤ 4) while the M7(AleThio)2 POMs are stable in alkaline medium (6 ≤ pH ≤ 13). Their cyclovoltammograms were recorded in solution. Attempts to surface immobilize the POMs through homo‐polymerization were unsuccessful but co‐polymerization employing 3‐methylthiophene led to polymeric films with covalently attached POMs.

No abstract

No abstract