Alkyl and non-alkyl cobaloximes with dimesitylglyoxime have been synthesized and characterized with 1 H and 13 C NMR, UV-vis, and X-ray diffraction. The X-ray structures of MeCo(dmestgH) 2 Py, ClCo(dmestgH) 2 Py, and BrCo(dmestgH) 2 Py are reported. The cis-trans influence has been studied by 1 H and 13 C NMR, UV-vis, and X-ray diffraction and is correlated with the reported cobaloximes. The spectral correlations are much better understood when both cobalt anisotropy and ring current are considered operating together. The trans influence of R/X has been monitored by the coordination shift of the Py γ proton/ carbon, and its chemical shift is a net result of the interplay of cobalt anisotropy and the trans effect of the R/X group. Two factors have been considered to study cis influence: (a) the effect of axial ligands on the equatorial dioxime moiety and (b) the effect of dioxime on the axial ligands. It is found that CdN and Py R are the most sensitive to any change in the molecule. A change in the axial R/X and dioxime moieties affects the CdN resonance, whereas Py R is sensitive to the change in R/X (trans effect) and the ring current of the dioxime (cis influence). A good correlation between δ( 13 C, CdN) and ∆δ( 1 H, Py R ) suggests the presence of ring current throughout the Co(dioxime) metallabicycle, and the negative slope indicates that they are effected in opposite directions. It is found that dmestgH complexes have the maximum cis influence among all the reported cobaloximes. A cyclic voltammetry study for both alkyl and non-alkyl cobaloximes is reported. The reduction from Co(III) to Co(II) and from Co(II) to Co(I) is found to be more difficult in ClCo(dmestgH) 2 Py as compared to the other chlorocobaloximes (gH, dmgH, dpgH).
Ion-selective electrodes (ISEs) with fluorous anion-exchanger membranes for the potentiometric detection of perfluorooctanoate (PFO(-)) and perfluorooctanesulfonate (PFOS(-)) were developed. Use of an anion-exchanger membrane doped with the tetraalkylphosphonium derivative (Rf8(CH2)2)(Rf6(CH2)2)3P(+) and an optimized measurement protocol resulted in detection limits of 2.3 × 10(-9) M (1.0 ppb) for PFO(-) and 8.6 × 10(-10) M (0.43 ppb) for PFOS(-). With their higher selectivity for PFO(-) over OH(-), membranes containing the alternative anion exchanger (Rf6(CH2)3)3PN(+)P((CH2)3Rf6)3 with a bis(phosphoranylidene)ammonium group further improved the detection limit for PFO(-) to 1.7 × 10(-10) M (0.070 ppb). These values are comparable with results obtained using well-established techniques such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and liquid chromatography-tandem mass spectrometry (LC-MS-MS), but the measurement with ISEs avoids lengthy sample preconcentration, can be performed in situ, and is less costly. Even when eventual spectrometric confirmation of analyte identity is required, prescreening of large numbers of samples or in situ monitoring with ISEs may be of substantial benefit. To demonstrate a real-life application of these electrodes, in situ measurements were performed of the adsorption of PFOS(-) onto Ottawa sand, which is a standard sample often used in environmental sciences. The results obtained are consistent with those from an earlier LC-MS study, validating the usefulness of these sensors for environmental studies. Moreover, PFOS(-) was successfully measured in a background of water from Carnegie Lake.
Manganese(III) complexes of three fluorophilic salen derivatives were used to prepare ion-selective electrodes (ISEs) with ionophore-doped fluorous sensing membranes. Because of their extremely low polarity and polarizability, fluorous media are not only chemically very inert but also solvate potentially interfering ions poorly, resulting in a much improved discrimination of such ions. Indeed, the new ISEs exhibited selectivities for CO32− that exceed those of previously reported ISEs based on non-fluorous membranes by several orders of magnitude. In particular, the interference from chloride and salicylate was reduced by two and six orders of magnitude, respectively. To achieve this, the selectivities of these ISEs were fine-tuned by addition of non-coordinating hydrophobic ions (i.e., ionic sites) into the sensing membranes. Stability constants of the anion–ionophore complexes were determined from the dependence of the potentiometric selectivities on the charge sign of the ionic sites and the molar ratio of ionic sites and the ionophore. For this purpose, a previously introduced fluorophilic tetraphenylborate and a novel fluorophilic cation with a bis(triphenylphosphoranylidene)ammonium group, (Rf6(CH2)3)3PN+P(Rf6(CH2)3)3, were utilized. The optimum CO32− selectivities were found for sensing membranes composed of anionic sites and ionophore in a 1:4 molar ratio, which results in the formation of 2:1 complexes with CO32− with stability constants up to 4.1 × 1015. As predicted by established theory, the site-to-ionophore ratios that provide optimum potentiometric selectivity depend on the stoichiometries of the complexes of both the primary and the interfering ions. However, the ionophores used in this study give examples of charges and stoichiometries previously neither explicitly predicted by theory nor shown by experiment. The exceptional selectivity of fluorous membranes doped with these carbonate ionophores suggests their use not only for potentiometric sensing but also for other types of sensors, such as the selective separation of carbonate from other anions and the sequestration of carbon dioxide.
A novel sandwich polyoxometalate
(POM) Na12[WCo3(H2O)2(CoW9O34)2] and poly(vinylimidazolium) cation
[PVIM+] in combination with nitrogen-doped carbon nanotubes
(NCNTs) was
developed for a highly selective and ultrasensitive detection of dopamine.
Conductively efficient heterogenization of Co5POM catalyst
by PVIM over NCNTs provides the synergy between PVIM–POM catalyst
and NCNTs as a conductive support which enhances the electron transport
at the electrode/electrolyte interface and eliminates the interference
of ascorbic acid (AA) at physiological pH (7.4). The novel PVIM–Co5POM/NCNT composite demonstrates a superior selectivity and
sensitivity with a lowest detection limit of 500 pM (0.0005 μM)
and a wide linear detection range of 0.0005–600 μM even
in the presence of higher concentration of AA (500 μM).
The key to unlock a renewable, clean, and energy-dense hydrogen fuel lies in designing an efficient oxygen evolving catalyst exhibiting high activity, stability, and cost-effectiveness. This report addresses an improved activity toward oxygen evolution by a composite of cobaltpolyoxometalate [Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] 10− (CoPOM) and an ionic polymer, poly(vinyl butyl imidazolium) (PVIM), in highly alkaline media. PVIM provides a stable platform for CoPOM and acts as a conductive linker between CoPOM and the electrode surface, forming a concrete solid composite, which balances the multinegative charge of CoPOM synergistically. This improved stability and conductivity of CoPOM by PVIM in the PVIM−CoPOM composite performs remarkable electrocatalytic water oxidation with a very low overpotential of 0.20 V and a very high current density of 250 mA/ cm 2 (at 1.75 V vs RHE) with a turnover frequency (TOF) of 52.8 s −1 in 1 M NaOH.
A polyoxometalate–ionic polymer composite was utilized as highly stable and efficient catalyst for high performance Li–S battery cathode with high utilization of sulfur and capacity retention.
The
composite of polyoxometalate [WZn3(H2O)2(ZnW9O34)2]12– (ZnPOM) with polyvinylidene-butyl-imidazolium cation
(PVIM) and oxidized carbon nanotubes (OCNT) as non-noble metal bifunctional
catalyst has been studied for oxygen-depolarized cathode (ODC) and
Cl2 evolution in HCl electrolysis for the first time. The
cyclic voltammetry and rotating disk electrode measurement analysis
reveals superior activity of the composite as bifunctional catalyst
for ODC and Cl2 evolution. Chronoamperometric experiments
show high long-term stability, comparable to the state-of-art catalyst,
even under multiple shutdown to open circuit potential. X-ray photoelectron
spectroscopic studies after electrolysis (48 h) confirms no degradation
of the composite and, hence, appears to be stable. Scanning electrochemical
microscopy (SECM) measurements indicate that, even after 72 h of electrolysis,
the composite retains high activity, similar to fresh composite.
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