PF6 Complexes Research Articles

A new crystal modification of diammonium hydrogen phosphate, (NH4)2(HPO4)

The addition of hexa­fluorido­phosphate salts (ammonium, silver, thallium or potassium) is usually used to precipitate complex cations from aqueous solutions. It has long been known that PF6 − is sensitive towards hydrolysis under acidic conditions [Gebala & Jones (1969 ▶). J. Inorg. Nucl. Chem. 31, 771–776; Plakhotnyk et al. (2005 ▶). J. Fluorine Chem. 126, 27–31]. During the course of our investigation into coinage metal complexes of diphosphine ligands, we used ammonium hexa­fluorido­phosphate in order to crystallize [Ag(diphos­phine)2]PF6 complexes. From these solutions we always obtained needle-like crystals which turned out to be the title compound, 2NH4 +·HPO4 2−. It was received as the hydrolysis product of NH4PF6. The crystals are a new modification of diammonium hydrogen phosphate. In contrast to the previously published polymorph [Khan et al. (1972 ▶). Acta Cryst. B28, 2065–2069], Z′ of the title compound is 2. In the new modification of the title compound, there are eight mol­ecules of (NH4)2(HPO4) in the unit cell. The structure consists of PO3OH and NH4 tetra­hedra, held together by O—H⋯O and N—H⋯O hydrogen bonds.

Synthesis, characterization and cytotoxic activities of the [RuCl2(NO)(dppp)(L)]PF6 complexes

The synthesis and characterization of ruthenium compounds of the type [RuCl(2)(NO)(dppp)(L)]PF(6) [dppp=1,3-bis(diphenylphosphino)propane; L=pyridine, 4-methylpyridine, 4-phenylpyridine and dimethyl sulfoxide] are described. The complexes were characterized by elemental analysis, UV/Vis and infrared spectroscopy, cyclic voltammetry, and X-ray crystallography for the complexes with the pyridine and 4-methylpyridine ligands. In vitro evaluation of these nitrosyl complexes revealed cytotoxic activity from 7.1 to 19.0 microM against the MDA-MB-231 breast tumor cells and showed that, in this case, they are more active than the reference metallodrug cisplatin. The 1,3-bis(diphenylphosphino)propane and the N-heterocyclic ligands alone failed to show cytotoxic activities at the concentrations tested (maximum concentration utilized=200 microM).

Effect of cyclopalladation on the spectroscopic properties of a Coumarin dye

The cyclopalladated [Pd(C6)Cl]2 and [Pd(C6)En]PF6 complexes based on Coumarin 6 are studied by 1H NMR spectroscopy and electronic absorption and emission spectroscopy. It is shown that cyclopalladation leads both to a long-wavelength shift of the spin-allowed intraligand absorption bands of coumarin and to the formation of a characteristic metal-ligand absorption band. It is found that, in comparison with coumarin, the complexes are characterized by a bathochromic shift and by a decrease in the fluorescence quantum yield due to more efficient intersystem crossing to the lower excited triplet state responsible for the low-temperature (77 K) phosphorescence of the complexes.

Tuning the Charge Distribution and Photoswitchable Properties of Cobalt–Dioxolene Complexes by Using Molecular Techniques

A series of cobalt complexes [Co(Me(n)tpa)(diox)]PF(6)sol (diox=3,5-di-tert-butyl-1,2-dioxolene; sol=ethanol, toluene; tpa=tris(2-pyridylmethyl)amine) were prepared by using tripod-like Me(n)tpa (n=0, 1, 2, 3), derived from tpa by successive introduction of methyl groups into the 6-position of the pyridine moieties, as an ancillary ligand. The steric hindrance induced by this substitution modulates the redox properties of the metal acceptor, thus determining the charge distribution of the metal-dioxolene moiety at room temperature. All of these complexes were characterised by using diffractometric studies, electronic spectroscopic analysis, and magnetic susceptibility measurements. In the solid state, the [Co(Me(n)tpa)(diox)](+) ions (n=0, 1) can be described as diamagnetic cobalt(III)-catecholato derivatives, whereas a cobalt(II)-semiquinonato description seems appropriate for the paramagnetic [Co(Me(3)tpa)(diox)](+) complex. The complex [Co(Me(2)tpa)(diox)]PF(6)C(2)H(5)OH undergoes entropy-driven valence tautomeric interconversion at room temperature. Optically induced valence tautomerism was observed by irradiation of [Co(Me(n)tpa)(diox)]PF(6) complexes (n=0, 1, 2) at cryogenic temperatures. The different relaxation kinetics of the photoinduced metastable phases are related to the respective free-energy changes of the interconversion, as estimated by cyclic voltammetric experiments at room temperature, and to the different lattice interactions, as supported by structural data. These results show the importance of molecular techniques for controlling the relaxation properties of photoinduced metastable species. At the same time, this behaviour strongly suggests that this paradigm exhibits intrinsic limits because of the less controllable factors that affect the process.

Sobre uma degenerescência acidental nos deslocamentos químicos de RMN de 31P{¹H} em complexos difosfínicos de rutênio

The [RuCl(bipy)(dppb)(4-pic)]PF6 complex was prepared and fully characterized. The X-ray crystal structure of this complex was determined in order to make an unambiguous distinction between the two possible positions of the 4-methylpyridine ligand (4-pic) in the compound: trans to phosphorus atom or trans to nitrogen atom. The [RuCl(bipy)(dppb)(4-pic)]PF6 complex exhibits an unusual temperature-dependent accidental degeneracy of the 31P chemical shifts in its solution NMR spectrum.

Buffer-Assisted Proton-Coupled Electron Transfer in a Model Rhenium−Tyrosine Complex

The mechanism for tyrosyl radical generation in the [Re(P-Y)(phen)(CO)3]PF6 complex is investigated with a multistate continuum theory for proton-coupled electron transfer (PCET) reactions. Both water and the phosphate buffer are considered as potential proton acceptors. The calculations indicate that the model in which the proton acceptor is the phosphate buffer species HPO(4)2- can successfully reproduce the experimentally observed pH dependence of the overall rate and H/D kinetic isotope effect, whereas the model in which the proton acceptor is water is not physically reasonable for this system. The phosphate buffer species HPO4(2-) is favored over water as the proton acceptor in part because the proton donor-acceptor distance is approximately 0.2 A smaller for the phosphate acceptor due to its negative charge. The physical quantities impacting the overall rate constant, including the reorganization energies, reaction free energies, activation free energies, and vibronic couplings for the various pairs of reactant/product vibronic states, are analyzed for both hydrogen and deuterium transfer. The dominant contribution to the rate arises from nonadiabatic transitions between the ground reactant vibronic state and the third product vibronic state for hydrogen transfer and the fourth product vibronic state for deuterium transfer. These contributions dominate over contributions from lower product states because of the larger vibronic coupling, which arises from the greater overlap between the reactant and product vibrational wave functions. These calculations provide insight into the fundamental mechanism of tyrosyl radical generation, which plays an important role in a wide range of biologically important processes.

Selective Low-Temperature Syntheses of Facial and Meridional Tris-cyclometalated Iridium(III) Complexes

We have developed a selective low-temperature synthesis of fac and mer tris-cyclometalated Ir(III) complexes. The chloro-bridged dimers [Ir(CwedgeN)2Cl]2 (CwedgeN = cyclometalating ligand) are cleaved in coordinating solvents like acetonitrile to give neutral Ir(CwedgeN)2(NCCH3)Cl species which in turn are reacted with AgPF6 to give hexafluorophosphate salts of the bis-acetonitrile species [Ir(CwedgeN)2(NCCH3)2]PF6 for CwedgeN = 2,2'-thienylpyridine (thpy) and 2-phenylpyridine (ppy). These bis-acetonitrile complexes are excellent starting materials for the synthesis of tris-Ir(III) complexes. The complexes of the general formula fac-Ir(CwedgeN)3 were synthesized with the ligands thpy and ppy at 100 degrees C in o-dichlorobenzene from the corresponding [Ir(CwedgeN)2(NCCH3)2]PF6 complexes. The reaction of [Ir(CwedgeN)2(NCCH3)2]PF6 with thpy at room temperature did not give the expected tris complex but instead gave [Ir(thpy)2(N,S-thpy)]PF6, with the third chelating ligand complexed through the sulfur atom of the thiophene ring. [Ir(thpy)2Cl]2, [Ir(ppy)2Cl]2, Ir(thpy)2(NCCH3)Cl, [Ir(thpy)2(NCCH3)2]PF6, [Ir(ppy)2(NCCH3)2]PF6, and [Ir(thpy)2(N,S-thpy)]PF6 were structurally characterized by X-ray crystallography. Additionally, hydroxy-bridged dimers, [Ir(CwedgeN)2(OH)]2, were synthesized as starting materials for the selective synthesis of mer-Ir(CwedgeN)3 complexes at 100 degrees C in o-dichlorobenzene. A mechanism is proposed that may account for the selectivity observed in the formation of the mer-Ir(CwedgeN)3 and fac-Ir(CwedgeN)3 isomers in previous studies and the studies presented here.

Metal−Halide Bond Photoactivation from a PtIII−AuII Complex

The d8···d10 heterobimetallic [PtIIAuI(dppm)2PhCl]PF6 (1) complex (dppm = bis(diphenylphosphino)methane) is oxidized by PhICl2 to give the d7−d9 [PtIIIAuII(dppm)2PhCl3]PF6 (2) complex containing a PtIII−AuII bond. Facile M−X bond activation is achieved by irradiation of CH3CN solutions of 2 with visible light in the presence of 2,3-dimethyl-1,3-butadiene, inducing a two-electron reduction to regenerate 1.

Coordination features of bis(N-heterocyclic carbenes) and bis(oxazolines) with 1,3-alkylidene-2,4,6-trimethylbenzene spacers. Synthesis of the ligands and silver and palladium complexes

The synthesis of simple imidazolium-based ligand precursors containing a 1,3-alkylidene-2,4,6-trimethylbenzene spacer was examined and different synthetic protocols were applied depending on the nature of the alkylidene arm. For a methylene arm, simple dications 5a,b.2CI were obtained directly. The higher homologue counterparts were conveniently prepared by general multistep routes following a five-step sequence for ethylene dications 6a,b.2Br or a six-step sequence for propylene dications 7a,b.2Br in > or = 52% overall yield. Imidazolium salts based on the shorter methylene spacer were used to prepare palladium complexes (17-20) with N-heterocyclic carbenes via transmetallation from well-defined silver compounds or directly in basic conditions. In order to facilitate spectroscopic characterisation of the palladium species two [Pd(allyl)(bis-oxazoline)]+ (25-26) complexes with the same ligand bridge were synthesized. [PdX2bisL] complexes appeared in solution as mixtures of species, mononuclear with cis- or trans-geometry or oligomeric compounds. The reaction of [PdCl(allyl)]2 and micro-bis(carbene)(AgX)2 complexes in 1 : 1 or in 0.5 : 1 ratio leads to binuclear compounds [Pd2Cl2(allyl)2(micro-bis-carbene)] (19a,19b) and to very labile monomeric [Pd(allyl)(bis-carbene)]+ (20a,20b) compounds, respectively. The preparation of analogous [Pd(allyl)(bis-oxazoline)]+ complexes showed the formation of one of the four possible isomers. [Pd(allyl)(bis-oxazoline)]PF6 complexes were inactive as catalytic precursors in the allylic substitution reaction.

Bis‐Ruthena(III)cycles [Ru(C∩N)2(N∩N)]PF6 as Low‐Potential Mediators for PQQ Alcohol Dehydrogenase (C∩N = 2‐phenylpyridinato or 4‐(2‐tolyl)pyridinato, N∩N = bpy or phen)

AbstractBis‐cyclometalated analogs of tris(2,2′‐bipyridine)ruthenium(II), namely [RuIII(C∩N)2(N∩N)]PF6 complexes 3, are prepared in 52–57 % yield from the mono‐cyclometalated N,N‐dimethylbenzylamine (dmbaH) derivatives [RuII(dmba)(N∩N)(MeCN)2]PF6 (N∩N = bpy or phen) and mercurated 2‐phenylpyridinato‐ or 4‐(2‐tolyl)pyridinato (C∩N) species Hg(C∩N)Cl. Two new bis‐ruthenacycles studied by X‐ray crystallography revealed a C1 symmetry, with the C and N atoms of different C∩N ligands trans to the nitrogen atoms of the N∩N ligand. The reduction potential of the RuII/III feature of 3 is as low as ca.–0.2 V (vs. SCE in MeCN). Complexes 3 display a unique mediating ability in moving electrons from the reduced active site of PQQ‐dependent alcohol dehydrogenase (PQQ‐ADH) to an electrode with 1,2‐propanediol as a substrate at a working potential of +0.1 V. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Polar Self‐Assembly: Steric Effects Leading to Polar Mixed‐Ligand Coordination Cages

We present a highly unusual example of self-assembly, specifically a polar, mixed-ligand cage which forms in preference to symmetrical homo-ligand products, and which suggests that steric effects can be exploited to obtain novel non-uniform polyhedral cages. In particular, reaction between the bulky tripodal triphosphine 2,4,6-tris(diphenylphosphino)triazine, L1, the non-bulky tripodal trinitrile 2,4,6-tris(cyanomethyl)trimethylbenzene, L2 and silver hexafluoroantimonate, AgSbF6, in a 3:1:4 ratio gives the mixed-ligand aggregate [Ag4(L1)3(L2)(SbF6)]3+, 1-SbF6, instantly as the only product in quantitative yield. The X-ray crystal structure of complex 1-SbF6 is consistent with the suspected solution-state structure. The cage derives from trigonal-pyramidal geometry, the basal vertices of which are defined by three bulky triphosphines, L1, and the apical vertex by the non-bulky trinitrile, L2. There is apical elongation amounting to 19% in comparison to the ideal uniform tetrahedron. The cage also encapsulates an SbF6 anion. 19F NMR spectra in solution for the analogous PF6 complex [Ag4(L1)3(L2)(PF6)]3+, 1-PF6, confirm that one anion is also encapsulated in solution. The synthesis of the analogous CF3SO3(-) complex, [Ag4(L1)3(L2)(OTf)]3+, 1-OTf, in solution is also described, although 1-PF6 and 1-OTf could not be isolated due to slow decomposition in solution. The selective formation of these mixed-ligand cages is discussed in terms of ligand-ligand and ligand-included anion steric repulsions, which we propose prevent the formation of the competing hypothetical homo-ligand tetrahedral structure [Ag4(L1)4(SbF6)]3+, and thus favour the mixed ligand cage. "Cage cone angles" for L1 and L2 are estimated at 115 degrees and 101 degrees, respectively. Variable-temperature 31P NMR spectroscopy shows that complex 1-SbF6 and the related previously reported partial tetrahedral complex [Ag4(L1)3(anion)]3+ undergo dynamic twisting processes in solution between enantiomeric C3-symmetry conformations.

Group 11 complexes with the bis(3,5-dimethylpyrazol-1-yl)methane ligand. How secondary bonds can influence the coordination environment of Ag(i): the role of coordinated water in [Ag2(µ-L)2(OH2)2](OTf)2

The complexation properties of the ligand bis(3,5-dimethylpyrazol-1-yl)methane (L) towards group 11 metals have been studied. The reaction in a 1 : 1 molar ratio with [Cu(NCMe)4]PF6 or Ag(OTf) complexes gives the mononuclear [CuL(NCMe)]PF6 (1), with crystallographic mirror symmetry, or dinuclear [Ag2(mu-L)2](OTf)2 (2) (OTf = trifluoromethanesulfonate) in which the ligand bridges both silver centres, an unprecedented mode of coordination for this type of ligands. Compound 2 crystallizes with two water molecules and forms a supramolecular structure through classical hydrogen bonding. The reaction in a 2 : 1 ratio affords in both cases the four-coordinated derivatives [ML2]X (M = Cu, X = PF6 (3); Ag, X = OTf 4). The treatment of [Ag(OTf)(PPh3)] with the ligand L gives [AgL(PPh3)]OTf (5). The gold(I) derivative [Au2(C6F5)2(mu-L)] (6) has also been obtained by reaction of L with two equivalents of [Au(C6F5)(tht)]. These complexes present a luminescent behaviour at low temperature; the emissions being mainly intraligand but enhanced after coordination of the metal. Compounds 1-4 have been characterized by X-ray crystallography. DFT studies showed that, in the silver complex 2, coordination of H2O to Ag in the binuclear complex is favoured by formation of a hydrogen-bonding network, involving the triflato anion, and releasing enough energy to allow distortion of the Ag2 framework.

Synthesis, characterization, and single crystal X-ray structures of [CoIII(acacen)(thioacetamide)2]ClO4 and [CoIII((BA)2en)(thioacetamide)2]PF6 — Solvatochromic properties of [CoIII(acacen)(thioacetamide)2]ClO4

The trans-[CoIII(acacen)(ta)2]ClO4 (1) and trans-[CoIII((BA)2en)(ta)2]PF6 (2) complexes, where H2acacen = bis(acetylacetone)ethylenediimine, H2(BA)2en = bis(benzoylacetone)ethylenediimine, and ta = thioacetamide, have been synthesized by a solid-state method, and characterized by elemental analyses, IR, UV–vis, and 1H NMR spectroscopy. The crystal and molecular structures of 1 and 2 were determined by X-ray crystallography. Both compounds crystallize in the monoclinic space group P2/n. The ClO4 and PF6 ions are both disordered, ClO4 on a twofold axis in 1 and PF6 on an inversion center in 2. Also bridging N-CH2-CH2-N is disordered in both compounds. The octahedral coordination of Co(III) is slightly distorted in both cases. The thioacetamide ligands are S-bonded and occupy the axial position. The IR, UV–vis, and 1H NMR spectra of the two complexes and their solvatochromic properties are also discussed. The longest wavelength absorption that appears at 517 nm for 1 and at 528 nm for 2 in chloroform is solvent dependent, and is assigned as a metal-mediated ligand-to-ligand charge transfer (LLCT).Key words: solid-state synthesis, thioactamide, Co(III) (Schiff base), crystal structure, solvatochromism, metal-mediated LLCT.

Low-dimensional Compounds Containing Cyano Groups. XI. Preparation, Crystal Structure and Properties of Two Copper(II) Dicyanamide Complexes with PF 6 − Anions

From the reaction mixtures containing Cu(NO3)2, Na[N(CN)2], KPF6 and 2,2′-bipyridine (bpy) or 1,10- phenanthroline (phen) in 1:1:1:2 molar ratios, [Cu(bpy)2N(CN)2][Cu(bpy)2(H2O)](PF6)3 (1b) and [Cu (phen)2N(CN)2]PF6 (1p) complexes were isolated. Measured i.r. spectra confirm the presence of all functional groups in both complexes and, moreover, they indicate monodentate coordination of dicyanamide through the cyano nitrogen atom in (1p). The structure of (1b) contains two crystallographically independent complex cations. In both, Cu is coordinated by two chelating bpy molecules, and either dicyanamide anion or water molecule fills the fifth position, completing the basal plane. The CuII atoms in (1p) are coordinated by two chelating phen ligands and by one dicyanamide anion in the equatorial plane. Hexafluorophosphate anions in (1b) and (1p) remain uncoordinated. Besides the ionic forces in both structures, the structure of (1b) is stabilized by strong O—H………F and O—H………N hydrogen bonds and, moreover, both structures are stabilized by weak C—H………F hydrogen bonds and possible π-π interactions between pyridine rings of bpy or phen molecules.

Interactions of Rh(III)−Dihydrido−Bis(phosphine) Complexes with Semicarbazones

Interaction of cis,trans,cis-[Rh(H)2(PR3)2(acetone)2]PF6 complexes (R = aryl or R3 = Ph2Me, Ph2Et) under H2 with E-semicarbazones gives the Rh(III)-dihydrido-bis(phosphine)-semicarbazone species cis,trans-[Rh(H)2(PR3)2{R'(R' ')C=N-N(H)CONH2}]PF6, where R' and R' ' are Ph, Et, or Me. The complexes are generally characterized by elemental analysis, 31P{1H} NMR, 1H NMR, and IR spectroscopies, and MS. X-ray analysis of three PPh3 complexes reveals chelation of E-semicarbazones by the imine-N atom and the carbonyl-O atom. In contrast, the corresponding reaction of [Rh(H)2(PPhMe2)2(acetone)2]PF6 with acetophenone semicarbazone gives the ortho-metalated-semicarbazone species cis-[RhH(PPhMe2)2{o-C6H4(Me)C=N-N(H)CONH2}]PF6. The X-ray structure of E-propiophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicarbazones was not observed even at 40 atm H2.

Interaction of rhodium(i) bisphosphine complexes with semicarbazones to give orthometallated rhodium(iii) complexes

Interaction of the cis-[Rh(PR3)2(Solv)2]PF6 complexes (R = Ar or R3 = Ph2Me, Solv — solvent) under Ar with semicarbazones bearing a phenyl group on the imine-C atom gives the rhodium(iii)-hydrido-bis(phosphine)-orthometallated semicarbazone species [RhH(PR3)2{(o-C6H4(R")C=N—N(H)CONH2}]PF6 (R" = Me or Et), which are characterized generally by elemental analysis, 31P{1H} and 1H NMR spectroscopy, and mass-spectrometry. The PPh3-containing complex with R" = Me, structurally characterized by X-ray analysis, reveals coordination of the semicarbazone by the ortho-C atom, the imine-N atom, and the amide-carbonyl group. For a semicarbazone containing no Ph group, the rhodium(i) complex [Rh(PR3)2(Et(Me)C=N—N(H)CONH2)]PF6, containing the η2-semicarbazone bonded via the imine-N and carbonyl, is formed. Attempts to hydrogenate the C=N moiety in the complexes or to catalytically hydrogenate the semicarbazones were unsuccessful.

A New Atropisomeric P,N Ligand for Rhodium‐Catalyzed Asymmetric Hydroboration.

AbstractFor Abstract see ChemInform Abstract in Full Text.

X-ray crystallographic and NMR spectroscopical characterization of intermediates in the Pd-catalyzed allylic substitution reaction with 4-substituted phosphinooxazolines. Correlation between intermediate structure and product configuration

The novel P,N-ligand 2-[2-(diphenylphosphino)phenyl]-4,5-dihydro-4-methyl-4-phenyloxazole (2a) has been synthesized. The corresponding [PdII(η3-diphenylallyl) (2a)]PF6 (3a) and [PdII(η3-1,3-dimethylallyl) (2a)]PF6 (4a) complexes have been studied by X-ray analysis and NMR spectroscopy. 3a exists as exo–syn–syn isomer in the solid state. In solution, the same isomer predominates. The X-ray structure of 4a reveals that the oxazoline ligand is coordinated in a pseudo-enantiomeric conformation compared with 3a. A syn–anti arrangement of the allyl substituents is favored in the solid state. NMR spectroscopical investigations suggest a formation of six isomers in solution due to endo–exo orientation of the allyl moiety and syn–anti isomerization of the methyl substituents. NMR data of [Pd0(η2-dimethylfumarate)(phosphinooxazoline)] complexes give evidence that two isomers exist in solution. The isomeric ratio is strongly dependent on the steric bulk of the oxazoline substituents. The solid state structures of [Pd0(η2-dmfu) (2c)] and [Pd0(η2-dmfu) (1a)] confirmed the structures of the main isomer found in solution. The asymmetric allylic substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate catalyzed by 3a proceeds with a selectivity of 97% ee. The ee induced by 2a in catalytic allylic substitution of 1-methylbutenyl acetate is moderate (18%). A comparison of the intermediate 4a and 5a as model of the actual olefinic intermediate suggests that the poor enantioselectivity achieved with ligand 2a is due to the preferred formation of anti-isomers of the allylic intermediate 4a and the conformational instability of the complex.

A new atropisomeric P,N ligand for rhodium-catalyzed asymmetric hydroboration.

A new optically active and large dihedral angle atropisomeric P,N ligand, pyphos, which contains a tertiary phosphine and pyridine moiety, was prepared and resolved through diastereomeric complexation with chiral palladium amine complexes. The hexafluorophosphate salt of the diastereomers were found to be separable by fractional recyrstallization, while the corresponding chloride salt did not. [Rh(COD)pyphos]PF(6) complex was synthesized by metalation of pyphos with [Rh(COD)Cl](2) followed by anion exchange with NH(4)PF(6) in excellent yield, and the target rhodium complex was characterized by single-crystal X-ray crystallography. The chiral cationic rhodium complex was utilized in the enantioselective hydroboration of vinylarenes. Excellent regioselectivity and good enantioselectivity were observed, and the ee values were found to be dependent on the electronic properties of para-substituted styrenes.

Renewable-surface sol-gel derived carbon ceramic electrode fabricated by [Ru(bpy)(tpy)Cl]PF6 and its application as an amperometric sensor for sulfide and sulfur oxoanions.

A highly sensitive and fast responding sensor for the determination of thiosulfate, sulfite, sulfide and dithionite is described. It consists of a chemically modified carbon ceramic composite electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF6 complex that was constructed by the sol-gel technique. A reversible redox couple of Ru(II)/Ru(III) was observed as a solute in acetonitrile solution and as a component of carbon based conducting composite electrode. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltametry, the apparent electron transfer rate constant (kappa(S)) and transfer coefficient (a) were determined by cyclic voltametry which were about 28 s(-1) and 0.43 respectively. Electrocatalytic oxidation of S(2-), SO3(2-), S2O4(2-) and S2O3(2-) were effective at the modified electrode at significantly reduced overpotentials and in the pH range 1-11. Optimum pH values for amperometric detection of thiosulfate, dithionite, sulfide and sulfite are 7, 9, 2 and 2. Under the optimized conditions the calibration curves are linear in the concentration ranges 1-500, 3-80, 2-90 and 1-100 microM for S2O3(2-), SO3(2-), S2- and S2O4(2-) determination. The detection limit (signal to noise is 3) and sensitivity are 0.5 and 12, 2.8 and 6, 1.6 and 8, and 0.65 microM and 80 nA microM(-1) for thiosulfate, sulfite, sulfide and dithionite detection. The modified carbon ceramic electrode doped with Ru-complex shows good reproducibility, a short response time (t < 2 s), remarkable long term stability (> 6 month) and especially good surface renewability by simple mechanical polishing (RSD for eight successive polishing is 2%). The advantages of this sulfur compound amperometric detector based on ruthenium doped CCE are high sensitivity, inherent stability at a broader pH range, excellent catalytic activity, less expense and simplicity of preparation in comparison with recently published papers. This sensor can be used as a chromatographic detector for analysis of sulfur derivatives.