Physico-chemical studies on thermal analyses of sodium hexa/carboxylato/ferrates/III/

The thermolysis of sodium hexa/benzoato/ferrate/III/, i. e. Na₃[Fe/C₆H₅COO/₆].4.5H₂O has been investigated at different temperatures in air using Mössbauer, infrared spectroscopic and derivatographic techniques /DTG, DTA, TG/. The thermal decomposition proceeds without the reduction of iron/III/. An increase in particle size of -Fe₂O₃ formed during thermolysis has been observed with increasing temperature. The end product, -NaFeO₂ is formed as a result of the solid state reaction between -Fe₂O₃ and sodium carbonate.     

Electrochemical oxidation of californium in carbonae solutions

The electrolysis of trivalent californium, terbium and praseodimium in 2M K₂CO₃ solutions at pH 13.2 results in a partial oxidation of the trivalent ions to a higher oxidation state. Absorption spectra of Cf/III/ in 1M HCLO₄ and in 2M K₂O₃ and that of oxidized californium in carbonate solution have been recorded. Incomplete oxidation is accounted to a reducing species generated at high anode potentials.     

Untersuchungen im System PO?WO?H2O?H3O+

Investigations in the System PO ? WO ? H₂O? H₃O⁺ By means of the molar ratio and Job'S method of continuous variations modified by us the composition of heteropolytungstates was determined using for the first time UV absorption spectroscopic techniques. For the case of the 1P:12W complex it is shown: In Na₂HPO₄ solutions acidified with HCl only the 12-tungstophosphate anion [PW₁₂O₄₀]^3? is formed. The complex formation in dependence on the acid degree Z is complete at Z = 23 H₃O⁺/12 WO = 1.92. For Z = 2.0 the consumption of H₃O⁺ has been calculated to be 5 moles H₃O⁺/1 mole HPO. Using Babko'S dilution method the stability constant of [PW₁₂O₄₀]^3? was determined to be β_k = 2.4 · 10¹² l² · mole^?2.     

Comparison of the kinetics of cathodic H2 evolution from the unhydrated H3O+ ion and its hydrated form H9O: Frequency factor effects and modes of activation

Experiments are described in which the kinetics of cathodic hydrogen evolution from the unhydrated H₃O⁺ ion in pure CF₃SO H₃O⁺ are compared with those from an aqueous solution of CF₃SO₃H where the proton is mainly in a fully hydrated state as H₉O. From the acid hydrate, which exists mainly as the ionic compound CF₃SOH₃O⁺, rates of H₂ evolution at Ni, Pt, and Hg electrodes, measured at a given overpotential or expressed as exchange current densities, are between about 3.5 and 20 times slower than those from the same electrolyte in dilute (1.0M) aqueous solution. Allowing for the concentration differences in these two types of system and double-layer effects, the rate constants are between about 9.4 and 216 times smaller for the reaction from H₃O⁺ than from H₉O at the above electrodes. The evaluation of apparent heats of activation for H₂ evolution from the two types of proton sources allows ratios of real frequency factors to be calculated for discharge from H₃O⁺ and H₉O. These data have a bearing on the theoretical conclusions regarding proton discharge mechanisms and show that frequency factor effects can be as important as activation energy differences in determining the rates of proton discharge from different proton sources. The results are discussed in terms of current ideas about electron and proton transfer in electrochemical reactions, the state of hydration of H⁺, and the role of discharge from paired CF₃SO and H₃O⁺ ions. In particular, the molecular mechanics of discharge of the proton from the molecular ion H₃O⁺ can be different from that from the fully hydrated H⁺ ion where many more HO- vibrational and librational modes can be involved in the process of activation of the H₉O entity.     

Oxygenation of Co(II) Complexes with Tripodal Ligands

The kinetics of O₂-uptake of five-coordinated Co²⁺/tren complexes (tren = 2,2′, 2″-tris(2-aminoethyl)amine) have been studied extensively. The kinetics of formation of (tren)Co(O₂, OH)Co(tren)³⁺ exhibits two steps. The rate law of O₂-addition, the first step, was of the form: rate = (k[H⁺] + kK_a)/([H⁺] + K_a) [Co(tren)²⁺][O₂]. Second-order rate constants k = 220 ± 19 M ^?1s^?1 and k = 1.8 ± .035 · 10³M ^?1s^?1 agreed well from O₂-uptake and (stopped-flow) spectrophotometric measurements. The protonation constant of the hydroxo complex obtained by equlibrium measurements (spectrophotometric and by pH-titration) in anaerobic conditions (pK_a = 10.03) agreed well with that derived from kinetic data (p K_a = 9.93); k and k are about a factor 100 smaller than those for the pseudooctahedral Co(trien) (H₂O). This and the fact that several other Co(II) complexes with five-coordinated geometry do not exhibit oxygen affinity led to the proposal that the oxygenation mechanism for Co²⁺/tren complexes involves fast preequilibria between Co(tren) (H₂O)²⁺ and Co(tren) (H₂O) and only the latter is assumed to be reactive. The enhanced rate at high pH is explained by rate determining H₂O-exchange in the O₂-addition step and the ability of coordinated OH^? to labilize the neighbouring H₂O. This mechanism is furthermore supported by the formation of one kinetically preferred isomer of the peroxo-bridged dicobalt(III) complex (O₂ cis to the tertiary N-atom) and the large negative activation entropy (?30 eu). The second step is the intramolecular bridging reaction: is independent of [Co(tren)²⁺] and [O₂] but exhibits a pH-dependence of the form k₃ = k′₃[H + ]/(K_a + [H⁺]); k_?3 ( = 5 · 10^?5 s^?1) was determined independently and from the two rate constants the equilibrium constant was calculated as ≈ 10⁵. The ligand combination as in Co(tren)²⁺ was shown to provide an excellent balance to form a reversible oxygen carrier; possible reasons for this are discussed.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

ESR Study of Nitroxide Radicals Generated from Triaz-2-en-1-ols

The triazenols 4-R¹? C₆H₄? N?N? N(OH)? R² ( 1 ), oxidized with t-BuO radicals, produced nitroxide radicals R¹? C₆H₄? N(O^?)? N?N(R²) ⁺O^? ( 5 ). The suggested radical structure was confirmed by ¹⁵N-labeling. The reaction of triazenols 1 with PbO₂ proceeded under N₂ elimination, in which case nitroxides R¹? C₆H₄? N(R₂)? O^?( 2 ) were observed as the final radical products. The intermediate R¹? C₆H radicals were identified by spin-trapping.     

Ein Wechsel des Strukturtyps in den Oxiden BaCoGd2O5, BaCoDy2O5 und BaCoY2O5

A Change of Structure Type in the Oxides BaCoGd₂O₅, BaCoDy₂O₅, and BaCoY₂O₅ (I) BaCoGd₂O₅, (II) BaCoDy₂O₅, and (III) BaCoY₂O₅ were prepared for the first time and examined by single crystal work. (I) and (II) belong to the BaNiLn₂O₅-type. (I): a = 3.770; b = 5.860; c = 11.620 Å; Z = 2; (II): a = 3.755; b = 5.798; c = 11.514 Å; Z = 2; space group D–Immm. (III) crystallizes in the BaCuLn₂O₅-type, space group D–Pnma, a = 12.287; b = 5.713; c = 7.067 Å; Z = 4. The coordination of Co²⁺ changes from (I, II) to (III) from octahedral to tetragonal pyramidal.     

Ab initio study of the reaction of CHO+ with H2O and NH3

An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed of the reactions of formyl and isoformyl cations with H₂O and NH₃, which play an important role in flame and interstellar chemistries. Two different confluent channels were located leading to CO+H₃O⁺/NH. The first one corresponds to the approach of the neutral molecule to the carbon atom of the cations. The second one leads to the direct proton transfer from the cations to the neutrals. At 900 K the separate products CO+H₃O⁺/NH are the most stable species along the Gibbs energy profiles for the processes. For the reaction with H₂O the reaction channel leading to HC(OH) (protonated formic acid) is disfavored with respect to the two CO+H₃O⁺ channels in agreement with the experimental evidence that H₃O⁺ is the major ion observed in hydrocarbon flames. According to our calculations, NH+H₂O are considerably more stable in Gibbs energy than NH₃+H₃O⁺;NH will predominate in the reaction zone when ammonia is added to CH₄+Ar diffusion flame, as experimentally observed. At 100 K the most stable structures are the intermediate complexes CO…HOH/HNH. Particularly the CO…HOH complex has a lifetime large enough to be detected and, therefore, could play a certain role in interstellar chemistry. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1432–1443, 1999     

Mössbauer study of ferric oxide particles as products of thermal decomposition of iron/III/benzoate

The products of the thermal decomposition in air of iron/III/benzoate [Fe₃/C₆H₅COO/₆/OH/₂]OH.H₂O have been studied using conventional thermal analysis, X-ray diffraction measurements and mainly Mössbauer spectroscopy. The decomposition occurs in the temperature range 200–350°C. It was possible to identify benzoic acid and ferric oxide as final products. Above 300°C, the observed ferric oxide showed a particle size distribution, which depends on the heating temperature and the heating time interval, as evidenced by the following detected phases: superparamagnetic -Fe₂O₃ and magnetically ordered state with crystal structure of the phases -Fe₂O₃ and -Fe₂O₃. Also, two iron/III/ benzoate complexes having four and three ligands within the coordination sphere are suggested as intermediate products.     

Phytoecdysteroids ofRhaponticum carthamoides

From the roots with rhizomes of the plantRhaponticum carthamoides Willd) Iljin Compositae), in addition to integristerone A, ecdysterone, polypodin B, 2-deoxyecdysterone, and 24(28)-dehydromakisterone A, we have isolated the new compounds ecdysteron3–2,3-monoacetonide (I), ecdysterone 20,22-monoacetonide (II)) and rhapisterone (III): I — C₃₀H₄₈O₇, mp 232–233° (ethyl acetate-methanol) [] _D ²⁰ +56.4±2° (c 0.0; methanol); II — C₃₀H₄₈O₇, mp 227–229° (ethyl acetate-methanol), [] _D ²⁰ +60.1±2° (c 1.3; methanol); III — C₂₉H₄₈O₇, mp, 241–242° (ethyl acetate-methanol), [] _D ²⁰ +30±2° (c 0.1; dioxane). The structure of (III) was established on the basis of spectral characteristics as 2, 3, 14, 20R, 22R, 23-5-stigmast-7-en-6-one. Details of the PMR, mass, and IR spectra of all the compounds and of the CD of rhapisterone are given.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 681–684, September–October, 1987.     

Crystal Structures of {[Cd(phen)](C6H8O4)3/3} and {[Cd(phen)](C7H10O4)3/3} · 2H2O with C6H10O4 = Adipic Acid and C7H12O4 = Pimelic Acid

Two coordination polymers {[Cd(phen)](C₆H₈O₄)_3/3} ( 1 ) and {[Cd(phen)](C₇H₁₀O₄)_3/3} · 2H₂O ( 2 ) were structurally characterized by single crystal X‐ray diffraction methods. In 1 (C2/c (no. 15), a = 16.169(2)Å, b = 15.485(2)Å, c = 14.044(2)Å, β = 112.701(8)°, U = 3243.9(7)ų, Z = 8), the Cd atoms are coordinated by two N atoms of one phen ligand and five O atoms of three adipato ligands to form mono‐capped trigonal prisms with d(Cd‐O) = 2.271‐2.583Å and d(Cd‐N) = 2.309, 2.390Å. The [Cd(phen)] moieties are bridged by adipato ligands to generate {[Cd(phen)](C₆H₈O₄)_3/3} chains, which, via interchain π—π stacking interactions, are assembled into layers. Complex 2 (P1¯(no. 2), a = 9.986(1)Å, b = 10.230(3)Å, c = 11.243(1)Å, α = 66.06(1)°, β = 87.20(1)°, γ = 66.71(1)°, U = 955.7(2)ų, Z = 2) consists of {[Cd(phen)](C₇H₁₀O₄)_3/3} chains and hydrogen bonded H₂O molecules. The Cd atoms are pentagonal bipyramidally coordinated by two N atoms of one phen ligand and five O atoms of three pimelato ligands with d(Cd‐O) = 2.213—2.721Å and d(Cd‐N) = 2.329, 2.372Å. Through interchain π—π stacking interactions, the {[Cd(phen)](C₇H₁₀O₄)_3/3} chains resulting from [Cd(phen)] moieties bridged by pimelato ligands are assembled in to layers, between which the hydrogen bonded H₂O molecules are sandwiched.     

Iridium(I) complex of chelating pyridine-2-thiolate ligand: Synthesis, reactivity, and application to the catalytic E-selective terminal alkyne dimerization via C-H activation

A novel iridium(I) complex bearing a chelate-coordinated pyridine-2-thiolate ligand [Ir(η²-SNC₅H₄)(PPh₃)₂] (2) was prepared by the reaction of iridium ethylene complex [IrCl(C₂H₄)(PPh₃)₂] (1) with lithium salt of pyridine-2-thiol (Li[SNC₅H₄]). On the treatment of iridium(I) complex 2 with chloroform, iridium(III) dichloro-complex [IrCl₂(η²-SNC₅H₄)(PPh₃)₂] (3) was formed. Reactions of complex 2 with methyldiphenylsilane, acetic acid, and p-tolylacetylene afforded iridium(III) hydride complexes [IrH(SiMePh₂)(η²-SNC₅H₄)(PPh₃)₂] (4), [IrH(O₂CCH₃)(η²-SNC₅H₄)(PPh₃)₂] (5), and [IrH(CC(p-tolyl))(η²-SNC₅H₄)(PPh₃)₂] (6), respectively. Complex 2 catalyzed dimerization of terminal alkynes leading to enynes (7) with high E-selectivity via C-H bond activation.     

Reactions of hydroxyl (HO•) and hydroperoxyl (HO) radicals generated chemically and photochemically with poly(ethylene oxide)

Poly(ethylene oxide) (poly(oxy-1,2-ethanediyl) is rapidly oxidized by hydroxyl (HO^?) and hydroperoxyl (HO) radicals generated by photolysis of hydrogen peroxide (H₂O₂) or by the catalytic decomposition of H₂O₂ by metallic silver. This process is accompanied by a chain scission during which the molecular weight decreases and the polydispersity changes. As a result of this process, the crystalline structure of poly(ethylene oxide) disappears, and the polymer becomes completely amorphous. © 1995 John Wiley & Sons, Inc.     

Oxidative Cleavage of S–S Bond During the Reduction of Tris(pyridine‐2‐carboxylato)manganese(III) by Dithionite in Sodium Picolinate–Picolinic Acid Buffer Medium

The reduction of tris(pyridine‐2‐carboxylato)manganese(III) by dithionite has been investigated within the temperature window 288–303 K and at pH range 5.22–6.10 in sodium picolinate–picolinic acid buffer medium. The reaction obeys the following stoichiometry: The reaction is described in terms of a mechanism that involves an initial complex formation between S₂O₄^2? and [Mn^III(C₅H₄NCO₂)₃] followed by S–S bond cleavage to give 2HSO₃^? and [Mn^II(C₅H₄NCO₂)₂(H₂O)₂] as the products via the formation of SO₂^●? radical anion. Kinetics and spectrophotometric evidences are cited in favor of the suggested mechanism. Thermodynamic parameters associated with the equilibrium step and the activation parameters with the rate‐determining step have been computed.     

U(IV)/LN(III) unexpected mixed site in polymetallic oxalato complexes. Part II. Substitution of U(IV) for Ln(III) in the new oxalates (N2H5)Ln(C2O4)2·nH2O (Ln=Nd, Gd)

Two new hydrazinium lanthanide(III) oxalates, (N₂H₅)[Nd(C₂O₄)₂(H₂O)]·4H₂O (1) and (N₂H₅)[Gd(C₂O₄)₂(H₂O)]·4.5H₂O (2) have been prepared and their crystal structures determined by single-crystal X-ray diffraction. The crystal structures were solved by the direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. Crystallographic data: 1, triclinic, space group , , b=9.762(4), , α=62.378(5), β=76.681(5), γ=73.858(5), Z=2, R₁=0.0335 for 172 parameters with 3430 reflections with I?2σ(I); 2, triclinic, space group , , b=9.51(3), , α=62.11(4), β=76.15(5), γ=73.73(5), Z=2, R₁=0.0325 for 172 parameters with 1742 reflections with I?2σ(I). The two isotypic structures are built from a three-dimensional (3D) arrangement of lanthanide and oxalate ions. The lanthanide atom is coordinated by eight oxygen atoms from four tetradentate oxalate ions and one aqua oxygen. Alternating lanthanide and oxalate ions form six-membered rings that delimit tunnels running down three directions and occupied by hydrazinium and water molecules. Starting from these lanthanide(III) compounds two isotypic mixed Ln(III)/U(IV) oxalates, (N₂H₅)_0.75[Nd_0.75U_0.25(C₂O₄)₂(H₂O)]·4.5H₂O (3) and (N₂H₅)_0.75[Gd_0.75U_0.25(C₂O₄)₂(H₂O)]·4H₂O (4), are obtained by partial substitution of Ln(III) by U(IV) in the nine-coordinated site, the charge excess being compensated by removal of monovalent ions from the tunnels. Finally, using Na⁺ gel, two mixed Ln(III)/U(IV) sodium oxalates, Na_0.5[Nd_0.5U_0.5(C₂O₄)₂(H₂O)]·3H₂O (5) and Na_0.65[Gd_0.65U_0.35(C₂O₄)₂(H₂O)]·4.5H₂O (6) have been obtained without any change in the 3D framework.     

Zur Struktur von zwei Hydraten des Natriumphenolats: C6H5ONa · H2O und C6H5ONa · 3 H2O

The Structures of two Hydrates of Sodium Phenoxide: C₆H₅ONa · H₂O and C₆H₅ONa · 3 H₂O In the monohydrate of sodium phenoxide sodium is coordinated by 4 oxygen atoms having an average distance Na? O of about 2.631 Å being arranged in form of a distorted tetrahedron. The oxygen atoms of water and phenoxid serve as bridging ligands. Hence, the structure can be considered as a network with a general formula [Na^[4]O]. Moreover, the oxygen atoms are linked via hydrogen bonding. In the trihydrate of sodium phenoxide sodium is surrounded with 5 oxygen atoms with an average distance of 2.39 Å forming a tetragonal pyramide. The oxygen of the phenoxide, however, does not participate in the coordination of the sodium ion. The coordination polyhedrons are connected by sharing edges and verteces. The resulting layer can be described by the general formula [Na^[5]O₂^[2]O^[2]O^[1]]. Via hydrogen bonding the phenoxide ions are attached to this layer.     

Chiral “P-N-P” ligands, (C20H12O2)PN(R)PY2 [R = CHMe2, Y = C6H5, OC6H5, OC6H4-4-Me, OC6H4-4-OMe or OC6H4-4-Bu] and their allyl palladium complexes

Chiral “P-N-P” ligands, (C₂₀H₁₂O₂)PN(R)PY₂ [R = CHMe₂, Y = C₆H₅ (1), OC₆H₅ (2), OC₆H₄-4-Me (3), OC₆H₄-4-OMe (4) or OC₆H₄-4-^tBu (5)] bearing the axially chiral 1,1′-binaphthyl-2,2′-dioxy moiety have been synthesised. Palladium allyl chemistry of two of these chiral ligands (1 and 2) has been investigated. The structures of isomeric η³-allyl palladium complexes, (R′ = Me or Ph; Y = C₆H₅ or OC₆H₅) have been elucidated by high field two-dimensional NMR spectroscopy. The solid state structure of [Pd(η³-1,3-Ph₂-C₃H₃){κ²-(racemic)-(C₂₀H₁₂O₂)PN(CHMe₂)PPh₂}](PF₆) has been determined by X-ray crystallography. Preliminary investigations show that the diphosphazanes, 1 and 2 function as efficient auxiliary ligands for catalytic allylic alkylation but give rise to only moderate levels of enantiomeric excess.     

Kinetics of acid catalyzed and Ag(I) catalyzed decomposition of peroxodisulfate in aqueous medium

The mechanism of acid catalyzed decomposition of peroxodisulfate, (S₂O) in aqueous perchlorate medium involves the hydrolysis of the species H₂S₂O₈ and HS₂O and the homolysis of the species H₂S₂O₈, HS₂O and S₂O at the O? O bond. The overall rate law when 1.4M > [HClO₄] > 0.1M is The constants k′ and k″ contain the hydrolysis and homolysis rate constants of HS₂O₈^? and H₂S₂O₈, respectively. With added Ag(I), the acid catalyzed and Ag(I) catalyzed reactions take place independently. Ag(I) catalyzed decomposition appears to involve the species AgS₂O (aq).     

A phosphate catalyzed reaction of iodine with hydrazine in aqueous solutions

Pulse radiolysis was utilized to study the kinetics of the iodine-hydrazine reaction in aqueous solutions containing phosphate buffer in the pH range 5.5 to 7. The reaction rate was found to be proportional to and [I^–]^–1, but did not show simple proportionality to [H⁺]^–1 and was considerably higher than that found earlier when the pH of solutions was adjusted with HClO₄ or H₃BO₃. The results are in a formal agreement with the assumption that in phosphate buffered solutions a complex N₂H₄. HPO ₄ ^2– is formed, reacting with I₂ with a rate constant which is greater than that ascribed earlier to the reaction of N₂H₄ with I₂/Ref. 1/.