Spectrophotometric and ESR methods of rhenium determination based on one electron photoreduction of Re(VII)

A possibility of photochemical reduction of Re(VII) to Re(VI) in mixture of concentrated sulfuric and hydrochloric acids has been demonstrated. The reaction mechanisms of Re(VII) photoreduction and Re^VIOCl₅ ^– complex decay have been considered from view point of acids and water content. The optimal conditions of Re^VIOCl₅ ^– stability have been found.Spectrophotometric and ESR methods of rhenium determination based on photochemical production of Re^VIOCl₅ ^– complex with the detection limit of 1g/ml have been proposed. Rhenium concentration in industrial sulfuric acid has been determined.     

One-electron oxidation of organic substrates by oxochloride complex of rhenium(VI) in hydrochloric acid solutions

Photoreduction reactions of Re(VII) in the presence of an electron donor — diphenylamine (DPA) and hydroquinone (HQ) in concentrated hydrochloric acid solutions — were studied using the pulse photolysis method. The short-lived complex of rhenium(VI) ReOCL₅ undergoes one-electron oxidation reactions with both DPA to form a cation-radical DPA^+. and with HQ to form a semiquinone radical. The decay of the cation-radicals DPA^+. proceeds by a second order reaction with the formation of a stable product (_max=590 nm)Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 365–368, May–June, 1987.     

Synthesis and structure of the 2-(chlorophenylazo)pyridine chelated tricarbonylrhenium(I) complex and its anion radical derivatives <Emphasis Type="Italic">via</Emphasis> electrochemical reduction

Reacting Re(CO)₅Cl with the azopyridine ligand (1) (L) in boiling benzene afford the complex Re(CO)₃Cl(L), (2) in excellent yield [L=2-(p-Cl-C₆H₄NN)C₅H₄N]. The chelation of the azopyridine ligand accompanied by displacement of the two carbon monoxide ligands furnish a five-membered chelate ring. Structure determination of complex (2) has revealed a distorted octahedral ReC₃N₂Cl coordination sphere. The Re–N(pyridine) and, Re–N(azo) distances are 2.158(3) and 2.153(6) Å respectively, and the N–N length [1.273(4) Å], implicate relatively weak Re-azo(π*) back–bonding. The Re(CO)₃Cl(L) lattice consists of C–H...Cl hydrogen bonding and Cl...O non-bonded interactions constituting a supramolecular network. Extended Hückel calculations reveal that the LUMO of Re(CO)₃Cl(L) is Ca. 57% azo in character. One-electron quasireversible electrochemical reduction of the complex occurs near −0.3 V versus Saturated Calomel electrode(s.c.e.) The redox orbital is believed to belong to the above noted LUMO. Electrogenerated Re(CO)₃Cl(L^•–) underwent spontaneous solvolytic chloride displacement in MeCN, resulting in the isolation of Re(CO)₃(MeCN)(L^•–). The latter complex in turn reacted with imidazole and triphenylphosphine, furnishing Re(CO)₃(C₃H₄N₂)(L^•–) and Re(CO)₃(PPh₃)(L^•–), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)₃Cl(L) but with shifts to lower frequencies by 10–20 cm⁻¹. All three radical anion systems are one-electron paramagnetic (1.7–1.8 μ_B). The unpaired electron is primarily localized on the azoheterocycle ligand in a predominantly azo-π* orbital, but a small metal contribution (^{185, 187}Re, I=5/2) is also present. Thus Re(CO)₃(MeCN)(L^•–) and Re(CO)₃(C₃H₄N₂)(L^•–) display six-line e.p.r. spectra (A ˜ 28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)₃(PPh₃)(L^•–) seven nearly equispaced lines are observed due to virtually equal coupling between the metal and ³¹P (I=&frac;) nuclei. The g-values of the radical species are slightly higher than the free-electron value of 2.0023.     

Coordination chemistry of di-2-pyridylketone. Synthesis, spectroscopic investigations, X-ray studies and DFT calculations of Re(III) and Re(V) complexes

The paper presents a combined experimental and computational study of Re(III) and Re(V) complexes containing di-2-pyridylketone and its gem-diol form – [ReCl₃(dpk-N,O)(PPh₃)] (1), [ReCl₃(dpk-N,N′)(OPPh₃)] (2) and [ReOBr₃(dpk-OH)]·2(dpkH⁺Br⁻) (3). All the complexes have been characterized spectroscopically and structurally (by single-crystal X-ray diffraction). The complex 2 has been additionally studied by magnetic measurement. The magnetic behavior of 2 is characteristic of mononuclear octahedral Re(III) complex with d⁴ low-spin (³T_1g ground state) and arise because of the large spin–orbit coupling (ζ = 2500 cm⁻¹), which gives diamagnetic ground state. DFT and time-dependent (TD)DFT calculations have been carried out for [ReCl₃(dpk-N,N′)(OPPh₃)] and [ReOBr₃(dpk-OH), and their UV–vis spectra have been discussed on this basis.     

Synthesis,reactivity and x-ray crystal structures of mixed thiazolato- or carboxylato- carbonyl(phosphine) rhenium(I) complexes

Summary The compound [Re(CO)₃(PPh₃)₂Cl] reacts with the lithium salt of thiazole derivatives (L¹H = 2-amino-benzothiazole, L²H = 2–N-methyl-aminothiazole, L³H = 2–N-phenylaminothiazole, L⁴H = 2–N-(4-methoxyphenyl)aminothiazole, L⁵H = 2–N(4-nitrophenyl)aminothiazole) to give [Re(CO)₂-(PPh₃)₂(L)]. The compounds have been characterized by elemental analysis, i.r. and¹H n.m.r. spectra. At room temperature [Re(CO)₂(PPh₃)(L²)] reacts with L⁶H (L⁶H = diphenylacetic acid), to give the carboxylato complex [Re(CO)₂ .The crystal structures of [Re(CO)₂(PPh₃)₂(L²)] (2) and [Re(CO)₂(PPh₃)₂(L⁶)] (6) were determined by x-ray crystallography. [Re(CO)₂(PPh₃)₂(L²)] crystallizes in the monoclinic space group P2₁/m witha = 9.16(1),b= 24.82(2),c =9.12(1) Å, and = 115.81(4)°; D_c = 1.56 g cm^–3for Z = 2.The structure was refined to a final R of 6.4%. The molecules have C_s symmetry. The rhenium atom is six-coordinate with approximately octahedral geometry. The anionic ligand is chelating through the nitrogen atoms and is strictly planar allowing delocalization of the -electron density. [Re(CO)₂(PPh₃)₂(L⁶)] (6) crystallizes in the monoclinic space group P2₁/n witha = 22.203(5),b = 18.651(5),c =10.653(3) Å, = 91.08(3)°, Dc = 1.47 g cm^–3 for Z = 4. The structure was refined to a final R of 4.7%. The complex is monomeric and the rhenium atom is distorted octahedral with two mutuallytrans PPh₃ ligands, twocis CO ligands and one chelating Ph₂CHCO ₂ ^– ion.     

Sorption and separation of some elements of nuclear importance using Chelex-100

Chelex-100, in the anionic form has been studied for its ability to perform selective separation and concentration of some metal ions of nuclear importance from mineral acid solutions. The sorption behavior of Zr(IV)–Nb(V), Mo(VI), Tc(VII), Te(IV) and U(VI) from solutions of hydrochloric and sulphuric acids on Chelex-100 has been studied under static and dynamic conditions. Mo(VI) and Tc(VII) have been concentrated on the resin from hydrochloric or sulphuric acid solutions at low acidities probably, as the anions MoO ₄ ^2– and TcO ₄ ^– , respectively. Te(IV) has been isolated from hydrochloric acid solutions of normalities 6 in the form of the anionic chloro complex TeCl ₆ ^2– . Optimum conditions for elution and separation of Mo(VI), Tc(VII), Te(IV) and U(VI) were recommended.     

Photolysis of [PtBr6]2– complex in frozen methanol matrix

Photochemistry of the [PtBr₆]^2– complex in the low-temperature methanol matrix (77 K) was studied by low-temperature spectrophotometry and ESR spectroscopy. The [PtBr₄]^2– complex is the main photolysis product. The mechanism of two-electron reduction of the platinum(IV) ion is proposed. The primary photochemical process is electron transfer from the solvent molecule to the photoexcited initial complex to form the intermediate radical complex ([PtBr₆]^3–...^·CH₂OH). The transfer of the second electron in the radical complex produces the final reaction products.     

Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

The¹³C kinetic isotope effect fractionation in the decarbonylation of lactic acid (LA) of natural isotopic composition by concentrated phosphpric acids (PA) and by 85% H₃PO₄ has been studied in the temperature interval of 60–150°C. The values of the¹³C₍₁₎ isotope effects in the decarbonylation of lactic acid in 100% H₃PO₄, in pyrophosphoric acid and in more concentrated phosphoric acids are intermediate between the values calculated assuming that the C₍₁₎–OH bond is broken in the rate-controllin gstep of dehydration and those calculated for rupture of the carbon-carbon bond in the transition state. In the temperature interval of 90–130°C the experimental¹³C fractionation factors determined in concentrated PA approach quite closely the¹³C fractionation corresponding to C₍₂₎–C₍₁₎ bond scission. the¹³C₍₁₎ kinetic isotope effects in the decarbonylation of LA in 85% orthophosphoric acid in the temperature range of 110–150°C coincide with the¹³C isotope effects calculated assuming that the frequency corresponding to the C₍₁₎–OH vibration is lost in the transition state of decarbonylation. A change of the mechanism of decarbonylation of LA in going from concentrated PA medium to 85% H₃PO₄ has been suggested. A possible secondary¹⁸O and a primary¹⁸O kinetic isotope effect in decarbonylation of lactic acid in phosphoric acids media have been discussed, too.     

A heteropolynuclear R2[S2WS2Re(O)(Cl)S2WS2] (R = PPh4 and Et4N) complex. The first example of a tetrathiometalate ligand co-ordinated to an oxo-metal core

A solution of [ReOCl3(PPh3)2] in benzene reacts with solid (NH4)2WS4, in the presence of traces of H2O, to give [ReOCl(WS4)2]2–, isolated as its PPh4 (1) and NEt4 (2) salts. Both (1) and (2) exhibit (Re=O) at ca. 930, (Re=Cl) at ca. 330 (W=S)t at ca. 495 and (W–S–Re) bridging vibration at ca. 460cm–1. The FAB mass spectrum of (1) shows a peak for [ReO(WS4)2]+(m/z=826 amu) in the positive mode and that for PPh4[ReOCl(WS4)]– (m/z=889amu) in the negative mode, confirming the suggested composition. This is the second example of a d2 metal ion forming a tetrathiometalate complex and also the first example of an oxometal ion (excepting those of W and Mo) forming a molecular complex with tetrathio- tungstate or -molybdate ligands.     

Photo-induced oxidation of aqueous solution of Na2[Mo(V)2O4EDTA] in neutral KBr and K2S2O8 medium

When an aqueous solution of Na₂[Mo(V)₂O₄EDTA] (ethylene diamine tetraacetate) was photolyzed in the presence of excess KBr and K₂S₂O₈ at neutral pH, the complex was found to be oxidized due to the reactions of Br ₂ ^–. and SO ₄ ^–. , respectively. Oxidation of the complex was also observed due to the reactions of the complex with radiolytically generated Br ₂ ^–. and SO ₄ ^–. radicals. When the oxidation of the complex with SO ₄ ^–. was conducted in an unbuffered solution, a chain reaction was observed in the oxidation of the complex. The time resolved kinetics for the formation and decay of different transient intermediates and the relevant rate constants were investigated with a flash photolysis technique, and a probable mechanism for the oxidation process was given.     

Rhenium. Part XIX. A new isothiocyanato complex of quadrivalent rhenium

Summary Reaction between K₂[ReI₆] and KSCN in boiling MeOH or in the melt gave [Re(NCS)₆]^2– and a weakly paramagnetic species, isolated as its Cs salt. Tl, Me₄N and other salts of this species have been isolated from the reaction medium of from the Cs salt by metathesis. On the basis of magnetic susceptibility and i.r. spectra the new complex has been formulated as [Re₂(NCS)₁₂]^4– containing metalmetal bond and no bridging thiocyanate. The Me₄N salt has also been isolated by bioling aqueous solutions of HReO₄ and HSCN and then adding Me₄NCL. A pyridinium salt, formulated as (pyH)₄[Re₂(NCS)₁₂], has been obtained by boiling [ReO₂py₄]NCS with aqueous HSCN. The two complex species [Re(NCS)₆]^2– and [Re₂(NCS)₁₂]^4– show distinctly different magnetic moment and electronic spectra.     

Formation and photochemistry of organic sulfur compound–chlorine atom complexes

Photochemical reactions of organic sulfur compounds (CH₃SCH₃, C₂H₅SCH₃ and C₂H₅SC₂H₅)–chlorine atom complexes have been studied using a combined pulse radiolysis-laser flash photolysis technique. Excitation of all complexes has resulted in photobleaching with a similar quantum yield (0.37±0.07), independent of solvent polarities and concentration of solutes. The results were compared with previous studies of the analogous dimethyl sulfoxide (DMSO)–Cl complexes. It is concluded that the significant change of photobleaching quantum yields of the excited DMSO–Cl complex observed in the DMSO-CCl₄ mixed solvent is mainly due to the specific solvation effect of DMSO for cations.     

Oxidative degradation of nitrogen-containing organic compounds: vaccum-ultraviolet (VUV) photolysis of aqueous solutions of 3-amino 5-methylisoxazole

The oxidative degradation of 3-amino 5-methyl isoxazole initiated by the VUV photolysis of water at 172 nm has been studied. Mineralization of CO₂, H₂O, NO ₃ ^– and NH ₄ ⁺ is more efficient when reductive conditions (argon saturated solutions) are favoured. Formation of compounds which cannot be completely oxidised to CO₂ is observed. Experiments performed under strictly oxidative conditions show higher yields of these inert compounds and, hence, incomplete mineralization. Cyanide was formed in concentrations lower than 5×10^–5 mol/l. In alkaline aqueous solutions, cyanide is completely transformed into CO ₃ ^2– , NH ₄ ⁺ and NO ₃ ^– during the irradiation time needed to mineralize the isoxazole. Therefore, cyanide does not present a potential risk for the use of the VUV photolysis for isoxazole degradation. Similarly, organic nitrogen is converted into both, NO ₃ ^– and NH ₄ ⁺ . The relative concentrations of the two ions depend on total irradiation time, oxygen saturation and reactor geometry. A sequence of reactions is proposed and discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Kinetics of the radiation chemical reactions of tervalent and quadrivalent actinides and lanthanides in carbonate solutions

The reactions of the ions of tervalent and quadrivalent actinides and lanthanides with hydrated electrons e_aq ^– and CO₃ ^– radicals in concentrated carbonate solutions have been studied by microsecond pulse radiolysis, using spectrophotometric recording of short-lived particles. It is shown that the rate of the reactions of e_aq ^– with carbonato complexes of Ce(IV), Pu(IV), and Np(IV) is controlled by diffusion. The carbonato complex of Eu(III) reacts with e_aq ^–appreciably more slowly. A linear relationship is obtained between the logarithm of the rate constant for the reactions of CO₃ ^– with the carbonato complexes of Am(III), Ce(III), and Pu(III) and the redox potential of the complexes. The rate of the reaction of CO₃ ^– with Np(III) in carbonate solutions is controlled by diffusion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 28–32, January, 1990.     

Halogenation of π-cyclopentadienyltricarbonylrhenium and π-cyclopentadienyl(triphenylphosphine)dicarbonylrhenium

Conclusions The following previously unknown rhenium semicoordinaticn compounds were synthesized: [-C₅H₅Re(CO)₂PPh₃Cl]⁺Cl^–, [-C₅H₅Re(CO)₃Cl]⁺Cl^–, [-C₅-H₅Re(CO)₂PPh₃Cl]⁺Be₄, [-C₅H₅Re(CO)Cl₂]⁺ [Re(CO)₄Cl₂]^–, and -C₅H₅Re(CO)₂I₂, the latter of which was separated into the cis and trans isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimlcheskaya, No. 2, pp. 408–413, February, 1981.The authors express their gratitude to V. F. Sizom, P. V. Petrovskii, and B. V. Lokshin for taking the mass, IR, and PMR spectra.     

Determination of tyrosine traces by adsorption voltammetry of its copper (II) complex

The electrochemical behavior of the copper-tyrosine complex has been studied by linear-sweep adsorption voltammetry. In 0.02 mol/L Na₂HPO₄ buffer solution (pH=9.6), the complex can be adsorped on a hanging mercury drop electrode and reduced at a peak potential of about –0.42 V (vs. SCE). The secondary derivative peak height is linear proportional to the concentration of tyrosine in the range 1.0×10^–7–5.0×10^–5 mol/L. The detection limit is 5×10^–8 mol/L.Project supported by the Provincial Science Foundation of Shandong Province     

Characterization of transient species and products in photochemical reactions of Re(dmb) (CO)3 Et with and without CO2

Transient FT-IR spectra of fac-Re(dmb)(CO)₃(Et) after laser excitation (355 nm) were investigated in THF under Ar and CO₂ atmospheres. The CO stretching bands of Re(dmb^⊙)(CO)₃(THF) grow (2008 and 1897 cm^?1) and those of Re(dmb)(CO)₃(Et) bleach (1987 and 1875 cm^?1) at times <1 μs, consistent with clean cleavage of the Re-Et bond. Under a CO₂ atmosphere, the long-lived radical (τ>100 ms) converts slowly to the formato complex Re(dmb)(CO)₃(OC(O)H) (2020, 1916, 1873 and 1630 cm^?1). When the solvent is slightly wet, the bicarbonato complex, Re(dmb)(CO)₃(OC(O)OH), is also observed after photolysis under CO₂.     

[Re(η2-CS3)4]3−, a new trithiocarbonate-containing rhenium(V) dodecahedral anion

The mononuclear complex (NMe₄)₃[Re(²-CS₃)₄] has been prepared by adding CS₂ to ReS^– ₄ in a mixture of MeOH and NH₃. During the reaction, Re^VII is reduced to Re^V, the measured diamagnetism (X = –3.04 × 10^–4cm³mol^–1) of the complex showing that the two added electrons are coupled. (NMe₄)₃[Re(²-CS₃)₄] crystallizes in the space group Fddd, a = 11.985(4) Å, b = 23.001(11) Å, c = 47.463(19) Å, V = 13085(9) ų. The reaction of CS₂ results in the formation of trithiocarbonates bonded to the rhenium in a dodecahedral geometry.     

Electrochemical vapor generation of selenium species after online photolysis and reduction by UV-irradiation under nano TiO<Subscript>2</Subscript> photocatalysis and its application to selenium speciation by HPLC coupled with atomic fluorescence spectrometry

An online UV photolysis and UV/TiO₂ photocatalysis reduction device (UV–UV/TiO₂ PCRD) and an electrochemical vapor generation (ECVG) cell have been used for the first time as an interface between high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS) for selenium speciation. The newly designed ECVG cell of approximately 115 L dead volume consists of a carbon fiber cathode and a platinum loop anode; the atomic hydrogen generated on the cathode was used to reduce selenium to vapor species for AFS determination. The noise was greatly reduced compared with that obtained by use of the UV–UV/TiO₂ PCRD–KBH₄–acid interface. The detection limits obtained for seleno-DL-cystine (SeCys), selenite (Se^IV), seleno-DL-methionine (SeMet), and selenate (Se^VI) were 2.1, 2.9, 4.3, and 3.5 ng mL^–1, respectively. The proposed method was successfully applied to the speciation of selenium in water-soluble extracts of garlic shoots cultured with different selenium species. The results obtained suggested that UV–UV/TiO₂ PCRD–ECVG should be an effective interface between HPLC and AFS for the speciation of elements amenable to vapor generation, and is superior to methods involving KBH₄.     

Thermal and photochemical interaction of octacyanometallates(IV), [M(CN)8]4− (M = Mo or W) in the presence of pyrazine

The interactions between [M(CN)₈]^4– (M = Mo or W) and pyrazine (pz) in the solid state and in aqueous solutions have been analysed. In strongly acidic solutions {pzH⁺, [M(CN)₈]^4–} ion pair formation is observed; the pyrazinium salts (pzH)₂(H₃O)₂[Mo(CN)₈]·0.5pz·3H₂O and (pzH)₂K(H₃O)[W(CN)₈]·H₂O have been isolated. The X-ray crystal structure of the latter, and the spectroscopic properties of both, are described. The [W(CN)₈]^4– anion is approximately square antiprismatic (D_4d), with different H-bond environments around the N atoms. The ligand-field photolysis of [M(CN)₈]^4– in the presence of pyrazine in neutral and alkaline solution results in the formation of tetracyanooxometallates(IV) in equilibrium with pentacyanooxometallates(IV) through the [M(CN)₇(pz)]^3– anions as intermediates. The formation of the [M(CN)₆(pz)₂]^2– ion, postulated in the literature to be the final product of the alkaline photolysis, has definitively been excluded.