Investigation of the Pronounced Medium Effects Observed in the Voltammetry of the Highly Charged Lacunary Anions [α‐SiW11O39]8‐ and [α‐PW11O39]7‐.

Guo, SiXuan; Mariotti, Andrew W A; Schlipf, Christine; Bond, Alan M.; Wedd, Anthony G.

doi:10.1002/chin.200702014

Cited by 5 publications

(5 citation statements)

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“…However, trace amounts of water in acetonitrile can have a significant effect on the electrochemical behavior of reduced POMs. 63 , 64 Therefore, we compared the CVs of PVMo in reaction acetonitrile and dry acetonitrile. Since acetonitrile can pick up small quantities of water from ambient air during laboratory manipulations, including argon purging, the dry acetonitrile CVs were conducted in the glovebox.…”

Section: Resultsmentioning

confidence: 99%

“…Finally, many studies show that in acetonitrile, on addition of an excess of a strong acid, such as trifluoromethanesulfonic acid, POMs undergo reduction by two-electron transfer PCET processes and all the peaks shift to more positive potentials. 63 , 66 , 74 , 75 In this work, an excess of RSH (2-mercaptoethanol) was used to probe the oxidation reaction. Since the pK a of 2-mercaptoethonal is 9.6 in water and the H + dissociation is significantly less favorable in acetonitrile, 76 RSH cannot perform as an acid to facilitate PCET processes under the conditions in this work.…”

Section: Resultsmentioning

confidence: 99%

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Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations

Geletii

Tang

et al. 2023

Inorg. Chem.

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A recent report established that the tetrabutylammonium (TBA) salt of hexavanadopolymolybdate TBA4H5[PMo6V6O40] (PV6Mo6 ) serves as the redox buffer with Cu(II) as a co-catalyst for aerobic deodorization of thiols in acetonitrile. Here, we document the profound impact of vanadium atom number (x = 0–4 and 6) in TBA salts of PV x Mo12–x O40 (3+x)– (PVMo) on this multicomponent catalytic system. The PVMo cyclic voltammetric peaks from 0 to −2000 mV vs Fc/Fc+ under catalytic conditions (acetonitrile, ambient T) are assigned and clarify that the redox buffering capability of the PVMo/Cu catalytic system derives from the number of steps, the number of electrons transferred each step, and the potential ranges of each step. All PVMo are reduced by varying numbers of electrons, from 1 to 6, in different reaction conditions. Significantly, PVMo with x ≤ 3 not only has much lower activity than when x > 3 (for example, the turnover frequencies (TOF) of PV3Mo9 and PV4Mo8 are 8.9 and 48 s–1, respectively) but also, unlike the latter, cannot maintain steady reduction states when the Mo atoms in these polyoxometalate (POMs) are also reduced. Stopped-flow kinetics measurements reveal that Mo atoms in Keggin PVMo exhibit much slower electron transfer rates than V atoms. There are two kinetic arguments: (a) In acetonitrile, the first formal potential of PMo12 is more positive than that of PVMo11 (−236 and −405 mV vs Fc/Fc+); however, the initial reduction rates are 1.06 × 10−4 s−1 and 0.036 s–1 for PMo12 and PVMo11 , respectively. (b) In aqueous sulfate buffer (pH = 2), a two-step kinetics is observed for PVMo11 and PV2Mo10 , where the first and second steps are assigned to reduction of the V and Mo centers, respectively. Since fast and reversible electron transfers are key for the redox buffering behavior, the slower electron transfer kinetics of Mo preclude these centers functioning in redox buffering that maintains the solution potential. We conclude that PVMo with more vanadium atoms allows the POM to undergo more and faster redox changes, which enables the POM to function as a redox buffer dictating far higher catalytic activity.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations

Geletii

Tang

et al. 2023

Inorg. Chem.

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“…POM protonation is known to contribute to redox potential dispersion of similar POM species exposed to acidic protons. 10,36 In this case, the presence of residual H + used to charge-balance the parent (TBA) 4 H 3 [PW 11 O 39 ] POM, carboxylic acid groups of organogermanium linkers from untethered POM Ge -COOH, or other adventitious sources could have each contributed to protonation of POMs during CV experiments. Redox features with similar characteristics as those observed in the CVs of n + -Si|POM Ge samples were also present in CVs of the solvated POM Ge -COOH species at glassy carbon working electrodes in dry MeCN containing 0.1 TBAPF 6 (Figure S4).…”

Section: Resultsmentioning

confidence: 99%

Covalent Attachment of Polyoxometalates to Passivated Si(111) Substrates: A Stable and Electronic Defect-Free Si|POM Platform

Gurrentz

Rose

2021

J. Phys. Chem. C

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Polyoxometalates (POMs) have been investigated as multiredox components in functional molecular materials, and as a result the significance of irreversible POM attachment on electrode surfaces has increased. Achieving covalent immobilization on high-quality silicon surfaces remains a challenge, however, as prevailing methods couple POMs to unpassivated hydrideterminated Si substrates, which are prone to deleterious surface oxidation. Herein, we demonstrate an improved approach for covalent POM immobilization via secondary functionalization of Si(111)-mixed monolayers. Specifically, a carboxylate-functionalized Keggin-type polyoxometalate, [PW 11 O 39 (Ge-(CH 2 ) 2 COOH)] 4− , was bound to phenylethylamine surface linkers on methylpassivated Si(111). Current−voltage (J−V) analysis of POM-modified n + -type Si electrodes revealed multiple discrete redox transitions (E 1/2,W1 = −880 mV; E 1/2,W2 = −1260 mV vs Fc/Fc + ). Both J−V (Laviron, k ET,W1 = 4 s −1 ) and electrochemical impedance spectroscopy (EIS) analyses (k ET,W1 = 5 s −1 and k ET,W2 = 6 s −1 ) revealed consistent interfacial electrontransfer kinetics that are commensurate with other Si|POM systems. Importantly, these electrodes were of such high electronic quality that photoelectrochemical function of POM-modified p-type Si photoelectrodes was displayed. An experimental photovoltage was observed for p-Si(111)|POM, and Mott−Schottky analysis (dark conditions) revealed a systematic increase in the barrier heights (Φ B ) of POM-modified p-Si photoelectrodes relative to control samples (ΔΦ B = 120 meV). However, non-ideal trends observed between ΔΦ B and ΔV on for the photoelectrochemical reduction of methyl viologen at these illuminated photoelectrodes revealed that the functional outcome of this Si|POM system is defined by a thermodynamic interplay between charge equilibration in the Si substrate and interfacial electric field effects of the POM molecular overlayer. These results thus provide a platform for the further development and study of POM-modified (photo)electrode systems.

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“…Simulation of the voltametric response of 2P can be achieved using reaction schemes which either involve an intermediate species formed en route to a more stable rearranged two-electron reduced product or where the second daughter product results from reactions following twoelectron reduction. The former reaction scheme corresponds to a six-membered double square scheme [25,26] and satisfactory reproduction of the cyclic voltammetry (CV) can be obtained using this approach (Supplementary Scheme S1, Supplementary Fig. S1).…”

Section: Electrochemistrymentioning

confidence: 99%

Impact of the 2Fe2P core geometry on the reduction chemistry of phosphido-bridged diiron hexacarbonyl compounds

et al. 2022

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The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectroelectrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe 2 (µ 2 -PPh 2 (CH 2 ) x PPh 2 )(CO) 6 , x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P-Fe-Fe-P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109° (DP) and a twisting of the Fe(CO) 3 fragments from an eclipsed geometry (2P, 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E 1 and E 2 ) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E 2 than E 1 and this impacts the stability of the monoanion with respect to disproportion (K disp (298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions.

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Investigation of the Pronounced Medium Effects Observed in the Voltammetry of the Highly Charged Lacunary Anions [α‐SiW₁₁O₃₉]^8‐ and [α‐PW₁₁O₃₉]^7‐.

Cited by 5 publications

References 1 publication

Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations

Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations

Covalent Attachment of Polyoxometalates to Passivated Si(111) Substrates: A Stable and Electronic Defect-Free Si|POM Platform

Impact of the 2Fe2P core geometry on the reduction chemistry of phosphido-bridged diiron hexacarbonyl compounds

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