Electrochemistry Of Compounds Research Articles

Electrochemistry of Cobalta Bis(dicarbollide) Ions Substituted at Carbon Atoms with Hydrophilic Alkylhydroxy and Carboxy Groups

In this study we explore the effect on the electrochemical signals in aqueous buffers of the presence of hydrophilic alkylhydroxy and carboxy groups on the carbon atoms of cobalta bis(dicarbollide) ions. The oxygen-containing exo-skeletal substituents of cobalta bis(dicarbollide) ions belong to the perspective building blocks that are considered for bioconjugation. Carbon substitution provides wider versatility and applicability in terms of the flexibility of possible chemical pathways. However, until recently, the electrochemistry of compounds substituted only on boron atoms could be studied, due to the unavailability of carbon-substituted congeners. In the present study, electrochemistry in aqueous phosphate buffers is considered along with the dependence of electrochemical response on pH and concentration. The compounds used show electrochemical signals around −1.3 and +1.1 V of similar or slightly higher intensities than in the parent cobalta bis(dicarbollide) ion. The signals at positive electrochemical potential correspond to irreversible oxidation of the boron cage (the C2B9 building block) and at negative potential correspond to the reversible redox process of (CoIII/CoII) at the central atom. Although the first signal is typically sharp and its potential can be altered by a number of substituents, the second signal is complex and is composed of three overlapping peaks. This signal shows sigmoidal character at higher concentrations and may be used as a diagnostic tool for aggregation in solution. Surprisingly enough, the observed effects of the site of substitution (boron or carbon) and between individual groups on the electrochemical response were insignificant. Therefore, the substitutions would preserve promising properties of the parent cage for redox labelling, but would not allow for the further tuning of signal position in the electrochemical window.

Fluorene-containing β-diketonato ligands and their Rhodium(I) complexes

In this study, the fluorene-group was added to metal complexes, via the easily synthesized β-diketonato ligand. This enables the incorporation of a fluorescent tag into a variety of metal complexes. Three fluorene-containing β-diketones (1–3) were synthesized, characterized and pKa-values determined. The synthesized ligands were complexed with rhodium(I) (4–6). The electrochemistry of compounds 1–6 were studied. The fluorene-group exhibits no electrochemical activity in the solvent window studied. The β-diketonato ligands showed an electrochemically reversible reduction of the ligand backbone at around −2000 mV vs ferrocene as an internal standard. The rhodium(I) complexes exhibited the same ligand reduction at around −2200 mV, with increased chemical reversibility, while the metal center was oxidized at ~300 mV, followed by solvent coordination forming a rhodium(III) species with reduction of this newly formed species at ~1300 mV. The absorbance and fluorescence of all synthesized complexes (1–6) were studied and fluorescence quantum yields were determined and found to be between 0.001 and 0.0001 as measured against anthracene as standard.

Electroanalysis and Spectroelectrochemistry of Nonaromatic Explosives in Acetonitrile Containing Dissolved Oxygen.

In search of a rapid, low-cost, and solution-phase detection technique for explosives, the (spectro-)electrochemistry of compounds from two major nonaromatic classes, namely nitramines (RDX and HMX) and nitrate esters (pentaerythritol tetranitrate (PETN) and the plastic explosive composite Semtex 1A) in acetonitrile (AN) is reported. In electrochemical screening, 5 μg of explosive material was detectable in 10 s by multicomponent cyclic voltammetric (CV) analysis on unmodified glassy carbon under ubiquitous environmental influences (i.e., trace water and dissolved oxygen). The explosives were identified with high recoveries under a battery of proof-of-concept testing scenarios in various matrices. In AN containing naturally dissolved oxygen (approx. 2 mM), the superoxide radical is co-electrogenerated during analyte reduction. Free superoxide yields prominent signals that the explosives attenuate quantitatively. To gain further insight into the electrochemical transformation mechanism, spectroelectrochemistry was employed to monitor changes in ultraviolet (UV) absorbance during CV and identify transient intermediates and product species, which could be targeted by future chemical sensors. Overlapping UV spectra of multiple species are deconvoluted using a new strategy, spectral regional baselining, for time- and potential-resolved spectroelectrochemical (SEC) analysis. This study shows that dissolved oxygen, hitherto an interferent purposefully removed from the solution, can be exploited advantageously in electrochemical sensing. The work expands our understanding of high-explosive solution-phase chemistry and offers a novel route to signal transduction for the sensing of energetic materials.

Supramolecular interaction-induced assemblies of polyanions and 2-aminopyridinium in two polyoxometalate-based hybrids.

Organic-inorganic hybrids consisting of organic cations and polyanions are promising functional materials due to their various compositions and structures. An important aspect of these materials is the interactions between the organic and inorganic components, which not only produce the final structures, but also influence the properties. Here, we investigated the interactions between organic cations and polyanions using protonated 2-aminopyridinium (Hap) as the cation, and successfully obtained two polyoxometalate-based hybrids, namely (C5H7N2)4[Mo8O26], (I), and (C5H7N2)2[NiMo6O16(OH)2{CH3C(CH2O)3}2]·4H2O, (II). In the crystal structure of (I), every Hap cation links with two polyanions by donating one or two N-H...O hydrogen bonds, and every polyanion is surrounded by eight Hap cations via terminal or bridging O atoms. Conversely, in compound (II), every Hap cation only links with one polyanion decorated by a triol ligand; this organic-inorganic component further assembles via uncoordinated water molecules. In the extended structures, Hap plays a key role, not only providing a counter charge, but also acting as `glue' linking polyanions in the role of hydrogen-bond donors. In both compounds, as the nodes of the supramolecular network, the polyanions exhibit an ordered two-dimensional arrangement due to strong hydrogen bonds and electrostatic interactions between the organic and inorganic parts. The electrochemistry of compound (I) shows that redox sourcing from polyanions is a surface-controlled process. Conversely, the magnetic behaviour of compound (II) indicates dominant antiferromagnetic properties.

Syntheses, characterization, and electrochemistry of compounds containing 1-diphenylphosphino-1′-(di-tert-butylphosphino)ferrocene (dppdtbpf)

The reaction of copper(I) salts CuX (X = Cl, Br, I, CN, SCN), [Cu(CH3CN)4]PF6 with 1-diphenylphosphino-1′-di-tert-butylphosphinoferrocene (dppdtbpf) in 1:1 M ratio in DCM–MeOH (50:50 V/V) at room temperature afforded mono and binuclear compounds having formula [Cu2(μ-Cl)2(κ2-P,P-dppdtbpf)2] (1), [Cu2(μ-Br)2(κ2-P,P-dppdtbpf)2] (2) [Cu2(μ-I)2(κ2-P,P-dppdtbpf)2] (3), [Cu2(μ-CN)2(κ2-P,P-dppdtbpf)2] (4), [Cu2(μ2-SCN)2(κ2-P,P-dppdtbpf)2] (5), and [Cu(κ2-P,P-dppdtbpf)(CH3CN)2]PF6 (6). Reacting palladium(II) complex [Pd(C6H5CN)2Cl2] with dppdtbpf gave mononuclear compound [Pd(κ2-P,P-dppdtbpf)Cl2] (7). The reaction of dppdtbpf with sulfur powder under reflux in chloroform afforded a ferrocene diphosphine disulfide dppSdtbpSf (8). All of the synthesized compounds were characterized by elemental analyses, IR, 1H and 31P NMR, ESI-MS and electronic absorption spectroscopy. Molecular structures for the compounds 5, 6, 7 and 8 were determined crystallographically. Compound 5 exists as centrosymmetric dimer in which the two copper atoms are bonded to two dppdtbpf ligands and two bridging thiocyanate groups in μ2-manner. In cationic compound 6, the copper atom is coordinated to one dppdtbpf ligand in κ2-manner and two acetonitrile molecules, whereas in 7, the palladium(II) adopted cis square-planar geometry by coordinating to one dppdtbpf ligand in κ2-manner and two chlorine atoms. Compound 8 revealed a sandwiched structure with both phosphine groups sulfurized. The electrochemical properties of 1–6 were studied by cyclic voltammetry. Compounds 1–6 exhibited moderately weak to strong luminescence properties, however compounds 7 and 8 are non-emissive in the solution state.

Soluble {[Rh 2(μ-OOCCH 3) 2(dbbpy) 2][BF 4]} n molecular wire and [Rh 2(μ-OOCCH 3) 2(dbbpy) 2L 2] 2+ complexes; dbbpy = 4,4′-di- tert-butyl-2,2′-bipyridine: Synthesis and physicochemical characterization

Binuclear Rh(II) compounds [Rh 2(μ-OOCCH 3) 2(dbbpy) 2(H 2O) 2](CH 3COO) 2 ( 1) (dbbpy = 4,4′-di- tert-butyl-2,2′-bipyridine), [Rh 2(μ-OOCCH 3) 2(dbbpy) 2(H 2O) 2](BF 4) 2·H 2O·CH 3CN ( 2), [Rh 2(CH 3COO) 2(C 18H 24N 2) 2(CH 3CN) 2](BF 4) 2·4CH 3CN ( 3) and {[Rh 2(μ-OOCCH 3) 2(dbbpy) 2][BF 4]} n ( 4) have been synthesized and characterized with spectroscopic methods. Structure of complex 3 has been determined using X-ray crystallography. Rhodium atoms in compound 3 have distorted octahedral coordination with O and N atoms in equatorial positions and Rh atom and CH 3CN molecule in axial coordination sites. Reduction of rhodium(II) compounds with aqueous 2-propanol leads to the formation of polymetallic compound {[Rh 2(μ-OOCCH 3) 2(dbbpy) 2][BF 4]} n ( 4) containing [Rh 2] 3+ core. Compound 4 shows strong antiferromagnetic properties, μ = 0.18–1.73 M.B. in the range 1.8–300 K, J = −597 cm −1. Electrochemistry of compounds 3 and 4 in CH 3CN has been investigated. Compound 4 exhibits a poorly reversible oxidation system at E 1/2 = −0.92 V (Δ E p = 0.19 V) and in solution in DMF is slowly oxidized to 3 even in total absence of oxygen. Complex 3 is irreversibly oxidized to Rh(III) compound at E pa = 1.48 V and irreversibly reduced at E pc = −1.02 V to lead to the unstable polynuclear complex 4 in CH 3CN.

Reactivity of tetracyanoquinodimethane with cobalt(II) chloride and bis(diphylphospino)methane in air

The reactions of CoCl 2·6H 2O, dppm (bis(diphenylphosphino)methane) and TCNQ (7,7,8,8-tetracyanoquinodimethane), with different ratios of the components, provided three new compounds, [Co(dppmdo) 3][TCNQ] 2 1 (dppmdo = P,P′-dioxo-bis(diphenylphosphinyl)methane), [Co(dppmdo) 3][(μ-TCNQ)-CoCl 3] 2, and [Co(dppmdo) 3][(μ-DCBE)-CoCl 3] 3 (DCBE = p-dicyanomethyl-benzoic ethyl ester). These products were characterized by IR, UV–Vis and UV–Vis-NIR spectra, X-ray crystallography, magnetic susceptibility measurements and cyclic voltammograms. 1 and 2 reveal low-energy transitions in the near-infrared region, which can be attributed to intra-ligand transitions involving radical anions (TCNQ/TCNQ −). It is interesting to note that, except for the redox potentials which are anodically shifted, indicating that it is easier to reduce TCNQ in 1 and 2 than the free TCNQ molecule, the electrochemistry of compounds 1 and 2 resemble that of the independent organic acceptor TCNQ. The magnetic properties suggest that an amount of electron transfer has occurred from the Co II complex, [Co(dppmdo) 3] 2+, to the TCNQ − anions in 1; an amount of electron transfer also has occurred from the Co II cation to the TCNQ − anion via a cyanide-bridge in 2; there is a mixture of spin transition of Co II ions and antiferromagnetic coupling between Co II ions in 3.

Synthesis, Structure and Electrochemistry of [Ru2(S2CNMe2)3(μ3-S2CNMe2)2]2[Mo6O19] · 2CH3COCH3

Reaction of MoO2(S2CNMe2)2 with RuCl3 ・χH2O in acetone at reflux afforded [Ru2(S2CNMe2)3- (μ3-S2CNMe2)2]2[Mo6O19]・2CH3COCH3 (1・2CH3COCH3) which was characterized by singlecrystal X-ray diffraction to show a dinuclear ruthenium-dithiocarbamate species as cation and hexamolybdate as counter anion. The [Ru2(S2CNMe2)3(μ3-S2CNMe2)2]+ cation may be considered as a combination of [Ru(S2CNMe2)3] with a cis-[Ru(S2CNMe2)2]+ species, and the Lindqvist anion [Mo6O19]2− is located on an inversion center between two cations. Spectroscopic properties along with the electrochemistry of compound 1・2CH3COCH3 are reported.

Synthesis and Structural and Physicochemical Characterization of {[Rh2(μ‐OOCCH3)2(dmbpy)2][BF4]}n Molecular Wire

AbstractDinuclear RhII compounds [Rh2(μ‐OOCCH3)2(dmbpy)2(H2O)2](CH3COO)2 (1) and [Rh2(μ‐OOCCH3)2(dmbpy)2(H2O)2](BF4)2·2.5H2O (2) (dmbpy = 4,4′‐dimethyl‐2,2′‐bipyridine) were synthesized and characterized with spectroscopic methods. The structure of complex 2 was determined by using X‐ray crystallography. The rhodium atoms in compound 2 have distorted octahedral coordination with O and N atoms in equatorial positions and a Rh atom and a H2O molecule in axial coordination sites. Reduction of compound 2 with aqueous alcohols leads to the formation of the molecular wire {[Rh2(μ‐OOCCH3)2(dmbpy)2][BF4]}n·2nH2O (3) containing a [Rh2]3+ core. Compound 3 shows strong antiferromagnetic properties, J = –780 cm–1 and μ = 0.128–1.349 B.M. in the range 1.8–300 K. The electrochemistry of compound 2 in acetonitrile was investigated. Complex 2 is irreversibly oxidized to a RhIII compound at Epa = 1.5 V and reduced to a wire with a [Rh4]6+ core at E1/2 = –0.87 V showing the same properties as those of the product obtained during chemical reduction.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Ruthenium cluster compounds containing 1,1′-bis(diphenylphosphino)ferrocene (dppf): an electrochemical analysis and the crystal structure of [Ru 3(CO) 11] 2(μ-dppf)

The electrochemistry of 1,1′-bis(diphenylphosphino)ferrocene (dppf) derivatives of Ru 3(CO) 12 was investigated. Two known compounds [Ru 3(CO) 8(μ-dppf) 2 ( 1) and Ru 3(CO) 10dppf ( 2)] and a new compound [Ru 3(CO) 11(μ-dppf)Ru 3(CO) 11 ( 3)] were prepared. Compound 3 was characterized spectroscopically and an X-ray crystal structure was obtained. The reductive electrochemistry of 1 and 2 showed an irreversible reduction and a follow-up oxidation, similar to Ru 3(CO) 12. The electrochemistry of compound 3 showed two irreversible waves and a follow-up oxidation. A trend in the reduction potential vs. the number of coordinated phosphorus atoms was noted. The oxidative electrochemistry of 1– 3 showed a dppf-based chemically reversible wave, and an irreversible wave similar to that of Ru 3(CO) 12. Trends were also noted between the oxidation potential and the number of coordinated phosphorus atoms.

Synthesis and electrochemistry of dimolybdenum crown ether imido complexes

The complexes [(η-MeC 5H 4) 4) 2Mo 2O 2(η-O){η-N(benzo-15-crown-5)}] ( 1) and [η-MeC 5H 4Mo-(O){η-N(benzo-15-crown-5)}] 2 ( 2) have been prepared by reaction of 4′-nitrobenzo-15-crown-5 with [(η-MeC 5H 4)Mo(CO) 3] 2. Compounds 1 and 2 react with phenyl isocyanate to yield [(η-MeC 5H 4) 2Mo 2(NPh) 2(μ-NPh){μ-N(benzo-5)}] ( 3) and [(η-MeC 5H 4)Mo(NPh){gm-N(benzo-15-crown-5)}] 2 ( 4) respectively. Acid hydrolysis of 3 yields [(η-MeC 5H 4) 2Mo 2O 2(η-Ph){η-N(benzo-15-crown-5)}] ( 5), whilst hydrolysis of 4 gives 2. The electrochemistry of compounds 1, 2 and 3 has been investigated by cryclic voltammetry in acetonitrile. Compound 1 undergoes an irreversible oxidation and an irreversible reduction. Compound 2 undergoes two irreversible oxidations, the first showing reversible behaviour at high scan rates, indicative of an EC mechanism. Compound 3 undergoes a reversible oxidation. Addition of excess sodium cations causes a significant anodic shift in the potential of this oxidation.

Transformation of a methyleneamide ligand at molybdenum: electrochemical oxidation to a cyanide, reactions with elemental oxygen, sulphur or selenium and X-ray crystal structures of trans-[Mo(CN)Cl(dppe)2]·MeOH and trans-[Mo(NCS)Cl(dppe)2]; electroreduction of the cyanide to an aminocarbyne, trans-[Mo(CNH2)Cl(dppe)2](dppe = Ph2PCH2CH2PPh2)

Deprotonation of the methylimide trans-[Mo(NMe)Cl(dppe)2]+(dppe = Ph2PCH2CH2PPh2) gives the reactive methyleneamide trans-[Mo(NCH2)Cl(dppe)2]A; oxidation of A at a platinum anode or by iodine gives trans-[Mo(CN)Cl(dppe)2]B, the structure of which has been determined by X-ray crystallography. Carbon-13 labelling studies suggest that the rearrangement of the MoNC framework to MoCN is intramolecular. Compound A reacts with chalcogens to give heterocumulene complexes trans-[Mo(NCX)Cl(dppe)2]C(X = O, S or Se), and the X-ray crystal structure of the sulphur derivative shows that the NCS ligand is N-bonded as an isothiocyanate. The electrochemistry of compound B is extensive: reduction under N2 gives trans-[Mo(N2)(CN)(dppe)2]– and in the presence of phenol affords the isolable aminocarbyne trans-[Mo(CNH2)Cl(dppe)2].

Synthesis, characterization, and electrochemistry of dicyclopentadienylsiloxane-bridged dicarbonyldi-iron

The new metal–metal bonded binuclear iron complexes [{Fe(CO)2}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][R = R′= Me, n= 1 (1) or 2 (2); R = Me, R′= Ph, n= 1 (3)] have been prepared in good yield by reaction between dicyclopentadienylsiloxanes, C5H5(RR′SiO)nSiRR′C5H5(R = R′= Me, n= 1 or 2; R = Me, R′= Ph, n= 1), and [Fe(CO)5]. Oxidation of (1)–(3) with [Fe(η5-C5H5)2]PF6 in the presence of PPh3 gives the dicationic complexes [{Fe(CO)2(PPh3)}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][PF6]2[R = R′= Me, n= 1 (7) or 2 (8); R = Me, R′= Ph,n= 1 (9)]. The dianionic complexes K2[{Fe(CO)2}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][R = R′= Me, n= 1 (10) or 2 (11); R = Me, R′= Ph, n= 1 (12)] were obtained by treating (1)–(3) with potassium diphenylketyl. The new binuclear iron complexes have been characterized by 1H and 13C n.m.r. and i.r. spectroscopy. The electrochemistry of compounds (1)–(3) indicates that two-electron oxidation products are stable on the voltammetric time-scale. Their kinetic stability depends upon the solvent donicity. The final products are dication complexes which do not contain carbonyl bridges (4)–(6).