Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

Abstract

Abstract[Os (bpy) indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os 2+/3+ redox states there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling. Apparatus and ProceduresThe reference electrode that was employed in organic solvents was a silver wire in contact IR SpectroscopyThe Differential pulse anodic stripping voltammetric (DPASV) experiments were performed so as to confirm the adsorption phenomenon observed in 0.01M electrolyte concentration. Figure 3 illustrates the DPASV of a modified carbon electrode in 0.1M Et 4 NPF 6 after an accumulation step at - As discussed in the previous section the oxidative processes of the Os 2+ centre exhibits characteristics pointing to an interaction between the complex and the electrode surface. As a result a film of the complex could be deposited onto the electrode surface by continuous redox switching through the osmium metal redox couple. Films were formed by cycling the potential of the glassy carbon electrode through the Os 3+/2+ redox process for 250 cycles from 9 a 0.1M TBAPF 6 DMSO solution of the starting complex. Figure 4 [79,80]. Despite the FWHM pointing to the first redox process being monoelectronic we believe it is bielectronic for two reasons. At slower scan rates a slight shoulder has been observed on the first redox process and it is well known that the first two monoelectronic processes are very close in potential. Secondly it is well know that the parent HPA can accept 6 electrons reversibly.The P 2 W 18 O 62 6-Dawson species is stable in pH's from 2.00 to 8.00 and its electrochemical behaviour depends upon the pH of the contacting electrolyte with some of the tungsten-oxo based redox processes involving protonation [75]. As a result we were interested in investigating the effect of solution pH on the redox activity of the film. With increasing pH, the losses. The lower stability of the film towards redox cycling in pH 4.50 is linked to the pH dependent nature of the tungsten-oxo reductions, when at more alkaline pH's the availability of protons which accompany the reductions is less, relative to that in pH 2.00. Scan rate studies were also performed at both pH 2.00 and 4.50, it was found that the peak potentials were independent of scan rate and th...

Ruthenium Metallopolymer: Dawson Polyoxomolybdate α-[Mo18O54(SO4)2]4– Adduct Films: Sensitization for Visible Photoelectrocatalysis

“…8−10 α/β-[W 18 O 54 (PO 4 ) 2 ] 6− has also been employed in electrocatalytic multilayer assemblies with [Fe(bpy) 3 ] 2+ and [Os(bpy) 3 ] 2+ . 11,12 A wide variety of other POMo-based multilayer systems using [Ru(bpy) 3 ] 2+ as the counterion have been reported and include α/β-[SiW 12 O 40 ] 4− , 13 [PMo 12 O 40 ] 3− , 14,15 [W 10 O 32 ] 4− , 16 and [Eu-(SiMo 9 W 2 O 39 ) 2 ] 13− . 17 In the majority of cases reported, these multilayers were employed as electrocatalysts for the reduction of small ions such as nitrate and nitrite, and photoelectrochemical applications have, to date, been relatively rare.…”

“…Significantly, the ratio of Ru to polyoxomolybdate centers in the composite film is 4.5 ± 0.2/1, which is higher than that found for adducts formed using monomeric complexes where the ratio corresponds exactly to full charge compensation at 2:1 or 3:1. 11,8,12,31 This behavior most likely arises because of the polymeric nature of the cation (i.e., extra ruthenium centers are bound to the polymeric chain that provides the two ruthenium centers needed to neutralize the charge on the POMo).…”

“…Polyoxometalates, POMs, are inorganic metal oxide anions that have very attractive photocatalytic and electrocatalytic properties. , Although much POM-based photocatalysis is typically performed in solution, there is significant interest in surface-immobilized thin films that often require novel hybrid materials. , POM-based thin films can be conveniently prepared via the Langmuir–Blodgett or a layer-by-layer (LBL) deposition method provided that a suitable cation is employed (e.g., transition-metal polypyridyl complexes). For example, multilayers of Dawson phosphotungstate α/β-[W 18 O 54 (PO 4 ) 2 ] 6– and [Ru(bpy) 3 ] 2+ have been built on a wide variety of substrates for use in electrocatalysis, electrochromism, and sensing. − α/β-[W 18 O 54 (PO 4 ) 2 ] 6– has also been employed in electrocatalytic multilayer assemblies with [Fe(bpy) 3 ] 2+ and [Os(bpy) 3 ] 2+ . , A wide variety of other POMo-based multilayer systems using [Ru(bpy) 3 ] 2+ as the counterion have been reported and include α/β-[SiW 12 O 40 ] 4– , [PMo 12 O 40 ] 3– , , [W 10 O 32 ] 4– , and [Eu(SiMo 9 W 2 O 39 ) 2 ] 13– . In the majority of cases reported, these multilayers were employed as electrocatalysts for the reduction of small ions such as nitrate and nitrite, and photoelectrochemical applications have, to date, been relatively rare.…”

Enhanced photocurrent production from thin films of Ru(ii) metallopolymer/Dawson polyoxotungstate adducts under visible irradiation

“…These data reveal that the ratio of Ru to polyoxotungstate or polyoxomolybdate 7 centres in the composite film is approximately (4.2 AE 0.2 : 1) indicating that the films contain a lower ruthenium content than that found for adducts formed using monomeric complexes where the ratio corresponds exactly to full charge compensation at 2 : 1 or 3 : 1. [10][11][12][13] Both films were stable to voltammetric cycling in their respective electrolytes, and the films were also stable in air over a period of a week. The peak currents for both the ruthenium and polyoxo centres increase linearly with the square root of the scan rate from 10 mV s À1 to 50 mV s À1 indicating that the system is under semi-infinite linear diffusion control under these conditions (Fig.…”

Self assembled composites of luminescent Ru(ii) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4−

“…Typically, in such complexes the metal complex cation and polyoxometalate anion combine in ratios in which the anion is fully charge compensated for by the cation. [6][7][8][9][10] The photophysics and photochemistry of a number of polyoxometalate-ruthenium polypyridyl electrostatic clusters have been reported both in solution and on surfaces, with the goal of characterizing electronic communication within the clusters. [11][12][13][14][15][16] More recently, electronic communication in some elegant examples of covalently linked Ru(II) polypyridyl and polyxometalates have also been reported.…”